3 \def\isabellecontext{Proof}%
10 \isacommand{theory}\isamarkupfalse%
12 \isakeyword{imports}\ Main\isanewline
21 \isamarkupchapter{Proofs \label{ch:proofs}%
25 \begin{isamarkuptext}%
26 Proof commands perform transitions of Isar/VM machine
27 configurations, which are block-structured, consisting of a stack of
28 nodes with three main components: logical proof context, current
29 facts, and open goals. Isar/VM transitions are typed according to
30 the following three different modes of operation:
34 \item \isa{{\isachardoublequote}proof{\isacharparenleft}prove{\isacharparenright}{\isachardoublequote}} means that a new goal has just been
35 stated that is now to be \emph{proven}; the next command may refine
36 it by some proof method, and enter a sub-proof to establish the
39 \item \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}{\isachardoublequote}} is like a nested theory mode: the
40 context may be augmented by \emph{stating} additional assumptions,
41 intermediate results etc.
43 \item \isa{{\isachardoublequote}proof{\isacharparenleft}chain{\isacharparenright}{\isachardoublequote}} is intermediate between \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}{\isachardoublequote}} and \isa{{\isachardoublequote}proof{\isacharparenleft}prove{\isacharparenright}{\isachardoublequote}}: existing facts (i.e.\
44 the contents of the special ``\indexref{}{fact}{this}\hyperlink{fact.this}{\mbox{\isa{this}}}'' register) have been
45 just picked up in order to be used when refining the goal claimed
50 The proof mode indicator may be understood as an instruction to the
51 writer, telling what kind of operation may be performed next. The
52 corresponding typings of proof commands restricts the shape of
53 well-formed proof texts to particular command sequences. So dynamic
54 arrangements of commands eventually turn out as static texts of a
57 \Appref{ap:refcard} gives a simplified grammar of the (extensible)
58 language emerging that way from the different types of proof
59 commands. The main ideas of the overall Isar framework are
60 explained in \chref{ch:isar-framework}.%
64 \isamarkupsection{Proof structure%
68 \isamarkupsubsection{Blocks%
72 \begin{isamarkuptext}%
73 \begin{matharray}{rcl}
74 \indexdef{}{command}{next}\hypertarget{command.next}{\hyperlink{command.next}{\mbox{\isa{\isacommand{next}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}state{\isacharparenright}{\isachardoublequote}} \\
75 \indexdef{}{command}{\{}\hypertarget{command.braceleft}{\hyperlink{command.braceleft}{\mbox{\isa{\isacommand{{\isacharbraceleft}}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}state{\isacharparenright}{\isachardoublequote}} \\
76 \indexdef{}{command}{\}}\hypertarget{command.braceright}{\hyperlink{command.braceright}{\mbox{\isa{\isacommand{{\isacharbraceright}}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}state{\isacharparenright}{\isachardoublequote}} \\
79 While Isar is inherently block-structured, opening and closing
80 blocks is mostly handled rather casually, with little explicit
81 user-intervention. Any local goal statement automatically opens
82 \emph{two} internal blocks, which are closed again when concluding
83 the sub-proof (by \hyperlink{command.qed}{\mbox{\isa{\isacommand{qed}}}} etc.). Sections of different
84 context within a sub-proof may be switched via \hyperlink{command.next}{\mbox{\isa{\isacommand{next}}}},
85 which is just a single block-close followed by block-open again.
86 The effect of \hyperlink{command.next}{\mbox{\isa{\isacommand{next}}}} is to reset the local proof context;
87 there is no goal focus involved here!
89 For slightly more advanced applications, there are explicit block
90 parentheses as well. These typically achieve a stronger forward
95 \item \hyperlink{command.next}{\mbox{\isa{\isacommand{next}}}} switches to a fresh block within a
96 sub-proof, resetting the local context to the initial one.
98 \item \hyperlink{command.braceleft}{\mbox{\isa{\isacommand{{\isacharbraceleft}}}}} and \hyperlink{command.braceright}{\mbox{\isa{\isacommand{{\isacharbraceright}}}}} explicitly open and close
99 blocks. Any current facts pass through ``\hyperlink{command.braceleft}{\mbox{\isa{\isacommand{{\isacharbraceleft}}}}}''
100 unchanged, while ``\hyperlink{command.braceright}{\mbox{\isa{\isacommand{{\isacharbraceright}}}}}'' causes any result to be
101 \emph{exported} into the enclosing context. Thus fixed variables
102 are generalized, assumptions discharged, and local definitions
103 unfolded (cf.\ \secref{sec:proof-context}). There is no difference
104 of \hyperlink{command.assume}{\mbox{\isa{\isacommand{assume}}}} and \hyperlink{command.presume}{\mbox{\isa{\isacommand{presume}}}} in this mode of
105 forward reasoning --- in contrast to plain backward reasoning with
106 the result exported at \hyperlink{command.show}{\mbox{\isa{\isacommand{show}}}} time.
112 \isamarkupsubsection{Omitting proofs%
116 \begin{isamarkuptext}%
117 \begin{matharray}{rcl}
118 \indexdef{}{command}{oops}\hypertarget{command.oops}{\hyperlink{command.oops}{\mbox{\isa{\isacommand{oops}}}}} & : & \isa{{\isachardoublequote}proof\ {\isasymrightarrow}\ local{\isacharunderscore}theory\ {\isacharbar}\ theory{\isachardoublequote}} \\
121 The \hyperlink{command.oops}{\mbox{\isa{\isacommand{oops}}}} command discontinues the current proof
122 attempt, while considering the partial proof text as properly
123 processed. This is conceptually quite different from ``faking''
124 actual proofs via \indexref{}{command}{sorry}\hyperlink{command.sorry}{\mbox{\isa{\isacommand{sorry}}}} (see
125 \secref{sec:proof-steps}): \hyperlink{command.oops}{\mbox{\isa{\isacommand{oops}}}} does not observe the
126 proof structure at all, but goes back right to the theory level.
127 Furthermore, \hyperlink{command.oops}{\mbox{\isa{\isacommand{oops}}}} does not produce any result theorem
128 --- there is no intended claim to be able to complete the proof
131 A typical application of \hyperlink{command.oops}{\mbox{\isa{\isacommand{oops}}}} is to explain Isar proofs
132 \emph{within} the system itself, in conjunction with the document
133 preparation tools of Isabelle described in \chref{ch:document-prep}.
134 Thus partial or even wrong proof attempts can be discussed in a
135 logically sound manner. Note that the Isabelle {\LaTeX} macros can
136 be easily adapted to print something like ``\isa{{\isachardoublequote}{\isasymdots}{\isachardoublequote}}'' instead of
137 the keyword ``\hyperlink{command.oops}{\mbox{\isa{\isacommand{oops}}}}''.
139 \medskip The \hyperlink{command.oops}{\mbox{\isa{\isacommand{oops}}}} command is undo-able, unlike
140 \indexref{}{command}{kill}\hyperlink{command.kill}{\mbox{\isa{\isacommand{kill}}}} (see \secref{sec:history}). The effect is to
141 get back to the theory just before the opening of the proof.%
145 \isamarkupsection{Statements%
149 \isamarkupsubsection{Context elements \label{sec:proof-context}%
153 \begin{isamarkuptext}%
154 \begin{matharray}{rcl}
155 \indexdef{}{command}{fix}\hypertarget{command.fix}{\hyperlink{command.fix}{\mbox{\isa{\isacommand{fix}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}state{\isacharparenright}{\isachardoublequote}} \\
156 \indexdef{}{command}{assume}\hypertarget{command.assume}{\hyperlink{command.assume}{\mbox{\isa{\isacommand{assume}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}state{\isacharparenright}{\isachardoublequote}} \\
157 \indexdef{}{command}{presume}\hypertarget{command.presume}{\hyperlink{command.presume}{\mbox{\isa{\isacommand{presume}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}state{\isacharparenright}{\isachardoublequote}} \\
158 \indexdef{}{command}{def}\hypertarget{command.def}{\hyperlink{command.def}{\mbox{\isa{\isacommand{def}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}state{\isacharparenright}{\isachardoublequote}} \\
161 The logical proof context consists of fixed variables and
162 assumptions. The former closely correspond to Skolem constants, or
163 meta-level universal quantification as provided by the Isabelle/Pure
164 logical framework. Introducing some \emph{arbitrary, but fixed}
165 variable via ``\hyperlink{command.fix}{\mbox{\isa{\isacommand{fix}}}}~\isa{x}'' results in a local value
166 that may be used in the subsequent proof as any other variable or
167 constant. Furthermore, any result \isa{{\isachardoublequote}{\isasymturnstile}\ {\isasymphi}{\isacharbrackleft}x{\isacharbrackright}{\isachardoublequote}} exported from
168 the context will be universally closed wrt.\ \isa{x} at the
169 outermost level: \isa{{\isachardoublequote}{\isasymturnstile}\ {\isasymAnd}x{\isachardot}\ {\isasymphi}{\isacharbrackleft}x{\isacharbrackright}{\isachardoublequote}} (this is expressed in normal
170 form using Isabelle's meta-variables).
172 Similarly, introducing some assumption \isa{{\isasymchi}} has two effects.
173 On the one hand, a local theorem is created that may be used as a
174 fact in subsequent proof steps. On the other hand, any result
175 \isa{{\isachardoublequote}{\isasymchi}\ {\isasymturnstile}\ {\isasymphi}{\isachardoublequote}} exported from the context becomes conditional wrt.\
176 the assumption: \isa{{\isachardoublequote}{\isasymturnstile}\ {\isasymchi}\ {\isasymLongrightarrow}\ {\isasymphi}{\isachardoublequote}}. Thus, solving an enclosing goal
177 using such a result would basically introduce a new subgoal stemming
178 from the assumption. How this situation is handled depends on the
179 version of assumption command used: while \hyperlink{command.assume}{\mbox{\isa{\isacommand{assume}}}}
180 insists on solving the subgoal by unification with some premise of
181 the goal, \hyperlink{command.presume}{\mbox{\isa{\isacommand{presume}}}} leaves the subgoal unchanged in order
182 to be proved later by the user.
184 Local definitions, introduced by ``\hyperlink{command.def}{\mbox{\isa{\isacommand{def}}}}~\isa{{\isachardoublequote}x\ {\isasymequiv}\ t{\isachardoublequote}}'', are achieved by combining ``\hyperlink{command.fix}{\mbox{\isa{\isacommand{fix}}}}~\isa{x}'' with
185 another version of assumption that causes any hypothetical equation
186 \isa{{\isachardoublequote}x\ {\isasymequiv}\ t{\isachardoublequote}} to be eliminated by the reflexivity rule. Thus,
187 exporting some result \isa{{\isachardoublequote}x\ {\isasymequiv}\ t\ {\isasymturnstile}\ {\isasymphi}{\isacharbrackleft}x{\isacharbrackright}{\isachardoublequote}} yields \isa{{\isachardoublequote}{\isasymturnstile}\ {\isasymphi}{\isacharbrackleft}t{\isacharbrackright}{\isachardoublequote}}.
192 ('assume' | 'presume') (props + 'and')
196 def: thmdecl? \\ name ('==' | equiv) term termpat?
202 \item \hyperlink{command.fix}{\mbox{\isa{\isacommand{fix}}}}~\isa{x} introduces a local variable \isa{x} that is \emph{arbitrary, but fixed.}
204 \item \hyperlink{command.assume}{\mbox{\isa{\isacommand{assume}}}}~\isa{{\isachardoublequote}a{\isacharcolon}\ {\isasymphi}{\isachardoublequote}} and \hyperlink{command.presume}{\mbox{\isa{\isacommand{presume}}}}~\isa{{\isachardoublequote}a{\isacharcolon}\ {\isasymphi}{\isachardoublequote}} introduce a local fact \isa{{\isachardoublequote}{\isasymphi}\ {\isasymturnstile}\ {\isasymphi}{\isachardoublequote}} by
205 assumption. Subsequent results applied to an enclosing goal (e.g.\
206 by \indexref{}{command}{show}\hyperlink{command.show}{\mbox{\isa{\isacommand{show}}}}) are handled as follows: \hyperlink{command.assume}{\mbox{\isa{\isacommand{assume}}}} expects to be able to unify with existing premises in the
207 goal, while \hyperlink{command.presume}{\mbox{\isa{\isacommand{presume}}}} leaves \isa{{\isasymphi}} as new subgoals.
209 Several lists of assumptions may be given (separated by
210 \indexref{}{keyword}{and}\hyperlink{keyword.and}{\mbox{\isa{\isakeyword{and}}}}; the resulting list of current facts consists
211 of all of these concatenated.
213 \item \hyperlink{command.def}{\mbox{\isa{\isacommand{def}}}}~\isa{{\isachardoublequote}x\ {\isasymequiv}\ t{\isachardoublequote}} introduces a local
214 (non-polymorphic) definition. In results exported from the context,
215 \isa{x} is replaced by \isa{t}. Basically, ``\hyperlink{command.def}{\mbox{\isa{\isacommand{def}}}}~\isa{{\isachardoublequote}x\ {\isasymequiv}\ t{\isachardoublequote}}'' abbreviates ``\hyperlink{command.fix}{\mbox{\isa{\isacommand{fix}}}}~\isa{x}~\hyperlink{command.assume}{\mbox{\isa{\isacommand{assume}}}}~\isa{{\isachardoublequote}x\ {\isasymequiv}\ t{\isachardoublequote}}'', with the resulting
216 hypothetical equation solved by reflexivity.
218 The default name for the definitional equation is \isa{x{\isacharunderscore}def}.
219 Several simultaneous definitions may be given at the same time.
223 The special name \indexref{}{fact}{prems}\hyperlink{fact.prems}{\mbox{\isa{prems}}} refers to all assumptions of the
224 current context as a list of theorems. This feature should be used
225 with great care! It is better avoided in final proof texts.%
229 \isamarkupsubsection{Term abbreviations \label{sec:term-abbrev}%
233 \begin{isamarkuptext}%
234 \begin{matharray}{rcl}
235 \indexdef{}{command}{let}\hypertarget{command.let}{\hyperlink{command.let}{\mbox{\isa{\isacommand{let}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}state{\isacharparenright}{\isachardoublequote}} \\
236 \indexdef{}{keyword}{is}\hypertarget{keyword.is}{\hyperlink{keyword.is}{\mbox{\isa{\isakeyword{is}}}}} & : & syntax \\
239 Abbreviations may be either bound by explicit \hyperlink{command.let}{\mbox{\isa{\isacommand{let}}}}~\isa{{\isachardoublequote}p\ {\isasymequiv}\ t{\isachardoublequote}} statements, or by annotating assumptions or
240 goal statements with a list of patterns ``\isa{{\isachardoublequote}{\isacharparenleft}{\isasymIS}\ p\isactrlsub {\isadigit{1}}\ {\isasymdots}\ p\isactrlsub n{\isacharparenright}{\isachardoublequote}}''. In both cases, higher-order matching is invoked to
241 bind extra-logical term variables, which may be either named
242 schematic variables of the form \isa{{\isacharquery}x}, or nameless dummies
243 ``\hyperlink{variable.underscore}{\mbox{\isa{{\isacharunderscore}}}}'' (underscore). Note that in the \hyperlink{command.let}{\mbox{\isa{\isacommand{let}}}}
244 form the patterns occur on the left-hand side, while the \hyperlink{keyword.is}{\mbox{\isa{\isakeyword{is}}}} patterns are in postfix position.
246 Polymorphism of term bindings is handled in Hindley-Milner style,
247 similar to ML. Type variables referring to local assumptions or
248 open goal statements are \emph{fixed}, while those of finished
249 results or bound by \hyperlink{command.let}{\mbox{\isa{\isacommand{let}}}} may occur in \emph{arbitrary}
250 instances later. Even though actual polymorphism should be rarely
251 used in practice, this mechanism is essential to achieve proper
252 incremental type-inference, as the user proceeds to build up the
253 Isar proof text from left to right.
255 \medskip Term abbreviations are quite different from local
256 definitions as introduced via \hyperlink{command.def}{\mbox{\isa{\isacommand{def}}}} (see
257 \secref{sec:proof-context}). The latter are visible within the
258 logic as actual equations, while abbreviations disappear during the
259 input process just after type checking. Also note that \hyperlink{command.def}{\mbox{\isa{\isacommand{def}}}} does not support polymorphism.
262 'let' ((term + 'and') '=' term + 'and')
266 The syntax of \hyperlink{keyword.is}{\mbox{\isa{\isakeyword{is}}}} patterns follows \railnonterm{termpat}
267 or \railnonterm{proppat} (see \secref{sec:term-decls}).
271 \item \hyperlink{command.let}{\mbox{\isa{\isacommand{let}}}}~\isa{{\isachardoublequote}p\isactrlsub {\isadigit{1}}\ {\isacharequal}\ t\isactrlsub {\isadigit{1}}\ {\isasymAND}\ {\isasymdots}\ p\isactrlsub n\ {\isacharequal}\ t\isactrlsub n{\isachardoublequote}} binds any
272 text variables in patterns \isa{{\isachardoublequote}p\isactrlsub {\isadigit{1}}{\isacharcomma}\ {\isasymdots}{\isacharcomma}\ p\isactrlsub n{\isachardoublequote}} by simultaneous
273 higher-order matching against terms \isa{{\isachardoublequote}t\isactrlsub {\isadigit{1}}{\isacharcomma}\ {\isasymdots}{\isacharcomma}\ t\isactrlsub n{\isachardoublequote}}.
275 \item \isa{{\isachardoublequote}{\isacharparenleft}{\isasymIS}\ p\isactrlsub {\isadigit{1}}\ {\isasymdots}\ p\isactrlsub n{\isacharparenright}{\isachardoublequote}} resembles \hyperlink{command.let}{\mbox{\isa{\isacommand{let}}}}, but
276 matches \isa{{\isachardoublequote}p\isactrlsub {\isadigit{1}}{\isacharcomma}\ {\isasymdots}{\isacharcomma}\ p\isactrlsub n{\isachardoublequote}} against the preceding statement. Also
277 note that \hyperlink{keyword.is}{\mbox{\isa{\isakeyword{is}}}} is not a separate command, but part of
278 others (such as \hyperlink{command.assume}{\mbox{\isa{\isacommand{assume}}}}, \hyperlink{command.have}{\mbox{\isa{\isacommand{have}}}} etc.).
282 Some \emph{implicit} term abbreviations\index{term abbreviations}
283 for goals and facts are available as well. For any open goal,
284 \indexref{}{variable}{thesis}\hyperlink{variable.thesis}{\mbox{\isa{thesis}}} refers to its object-level statement,
285 abstracted over any meta-level parameters (if present). Likewise,
286 \indexref{}{variable}{this}\hyperlink{variable.this}{\mbox{\isa{this}}} is bound for fact statements resulting from
287 assumptions or finished goals. In case \hyperlink{variable.this}{\mbox{\isa{this}}} refers to
288 an object-logic statement that is an application \isa{{\isachardoublequote}f\ t{\isachardoublequote}}, then
289 \isa{t} is bound to the special text variable ``\hyperlink{variable.dots}{\mbox{\isa{{\isasymdots}}}}''
290 (three dots). The canonical application of this convenience are
291 calculational proofs (see \secref{sec:calculation}).%
295 \isamarkupsubsection{Facts and forward chaining%
299 \begin{isamarkuptext}%
300 \begin{matharray}{rcl}
301 \indexdef{}{command}{note}\hypertarget{command.note}{\hyperlink{command.note}{\mbox{\isa{\isacommand{note}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}state{\isacharparenright}{\isachardoublequote}} \\
302 \indexdef{}{command}{then}\hypertarget{command.then}{\hyperlink{command.then}{\mbox{\isa{\isacommand{then}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}chain{\isacharparenright}{\isachardoublequote}} \\
303 \indexdef{}{command}{from}\hypertarget{command.from}{\hyperlink{command.from}{\mbox{\isa{\isacommand{from}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}chain{\isacharparenright}{\isachardoublequote}} \\
304 \indexdef{}{command}{with}\hypertarget{command.with}{\hyperlink{command.with}{\mbox{\isa{\isacommand{with}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}chain{\isacharparenright}{\isachardoublequote}} \\
305 \indexdef{}{command}{using}\hypertarget{command.using}{\hyperlink{command.using}{\mbox{\isa{\isacommand{using}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}prove{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}prove{\isacharparenright}{\isachardoublequote}} \\
306 \indexdef{}{command}{unfolding}\hypertarget{command.unfolding}{\hyperlink{command.unfolding}{\mbox{\isa{\isacommand{unfolding}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}prove{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}prove{\isacharparenright}{\isachardoublequote}} \\
309 New facts are established either by assumption or proof of local
310 statements. Any fact will usually be involved in further proofs,
311 either as explicit arguments of proof methods, or when forward
312 chaining towards the next goal via \hyperlink{command.then}{\mbox{\isa{\isacommand{then}}}} (and variants);
313 \hyperlink{command.from}{\mbox{\isa{\isacommand{from}}}} and \hyperlink{command.with}{\mbox{\isa{\isacommand{with}}}} are composite forms
314 involving \hyperlink{command.note}{\mbox{\isa{\isacommand{note}}}}. The \hyperlink{command.using}{\mbox{\isa{\isacommand{using}}}} elements
315 augments the collection of used facts \emph{after} a goal has been
316 stated. Note that the special theorem name \indexref{}{fact}{this}\hyperlink{fact.this}{\mbox{\isa{this}}} refers
317 to the most recently established facts, but only \emph{before}
318 issuing a follow-up claim.
321 'note' (thmdef? thmrefs + 'and')
323 ('from' | 'with' | 'using' | 'unfolding') (thmrefs + 'and')
329 \item \hyperlink{command.note}{\mbox{\isa{\isacommand{note}}}}~\isa{{\isachardoublequote}a\ {\isacharequal}\ b\isactrlsub {\isadigit{1}}\ {\isasymdots}\ b\isactrlsub n{\isachardoublequote}} recalls existing facts
330 \isa{{\isachardoublequote}b\isactrlsub {\isadigit{1}}{\isacharcomma}\ {\isasymdots}{\isacharcomma}\ b\isactrlsub n{\isachardoublequote}}, binding the result as \isa{a}. Note that
331 attributes may be involved as well, both on the left and right hand
334 \item \hyperlink{command.then}{\mbox{\isa{\isacommand{then}}}} indicates forward chaining by the current
335 facts in order to establish the goal to be claimed next. The
336 initial proof method invoked to refine that will be offered the
337 facts to do ``anything appropriate'' (see also
338 \secref{sec:proof-steps}). For example, method \indexref{}{method}{rule}\hyperlink{method.rule}{\mbox{\isa{rule}}}
339 (see \secref{sec:pure-meth-att}) would typically do an elimination
340 rather than an introduction. Automatic methods usually insert the
341 facts into the goal state before operation. This provides a simple
342 scheme to control relevance of facts in automated proof search.
344 \item \hyperlink{command.from}{\mbox{\isa{\isacommand{from}}}}~\isa{b} abbreviates ``\hyperlink{command.note}{\mbox{\isa{\isacommand{note}}}}~\isa{b}~\hyperlink{command.then}{\mbox{\isa{\isacommand{then}}}}''; thus \hyperlink{command.then}{\mbox{\isa{\isacommand{then}}}} is
345 equivalent to ``\hyperlink{command.from}{\mbox{\isa{\isacommand{from}}}}~\isa{this}''.
347 \item \hyperlink{command.with}{\mbox{\isa{\isacommand{with}}}}~\isa{{\isachardoublequote}b\isactrlsub {\isadigit{1}}\ {\isasymdots}\ b\isactrlsub n{\isachardoublequote}} abbreviates ``\hyperlink{command.from}{\mbox{\isa{\isacommand{from}}}}~\isa{{\isachardoublequote}b\isactrlsub {\isadigit{1}}\ {\isasymdots}\ b\isactrlsub n\ {\isasymAND}\ this{\isachardoublequote}}''; thus the forward chaining
348 is from earlier facts together with the current ones.
350 \item \hyperlink{command.using}{\mbox{\isa{\isacommand{using}}}}~\isa{{\isachardoublequote}b\isactrlsub {\isadigit{1}}\ {\isasymdots}\ b\isactrlsub n{\isachardoublequote}} augments the facts being
351 currently indicated for use by a subsequent refinement step (such as
352 \indexref{}{command}{apply}\hyperlink{command.apply}{\mbox{\isa{\isacommand{apply}}}} or \indexref{}{command}{proof}\hyperlink{command.proof}{\mbox{\isa{\isacommand{proof}}}}).
354 \item \hyperlink{command.unfolding}{\mbox{\isa{\isacommand{unfolding}}}}~\isa{{\isachardoublequote}b\isactrlsub {\isadigit{1}}\ {\isasymdots}\ b\isactrlsub n{\isachardoublequote}} is structurally
355 similar to \hyperlink{command.using}{\mbox{\isa{\isacommand{using}}}}, but unfolds definitional equations
356 \isa{{\isachardoublequote}b\isactrlsub {\isadigit{1}}{\isacharcomma}\ {\isasymdots}\ b\isactrlsub n{\isachardoublequote}} throughout the goal state and facts.
360 Forward chaining with an empty list of theorems is the same as not
361 chaining at all. Thus ``\hyperlink{command.from}{\mbox{\isa{\isacommand{from}}}}~\isa{nothing}'' has no
362 effect apart from entering \isa{{\isachardoublequote}prove{\isacharparenleft}chain{\isacharparenright}{\isachardoublequote}} mode, since
363 \indexref{}{fact}{nothing}\hyperlink{fact.nothing}{\mbox{\isa{nothing}}} is bound to the empty list of theorems.
365 Basic proof methods (such as \indexref{}{method}{rule}\hyperlink{method.rule}{\mbox{\isa{rule}}}) expect multiple
366 facts to be given in their proper order, corresponding to a prefix
367 of the premises of the rule involved. Note that positions may be
368 easily skipped using something like \hyperlink{command.from}{\mbox{\isa{\isacommand{from}}}}~\isa{{\isachardoublequote}{\isacharunderscore}\ {\isasymAND}\ a\ {\isasymAND}\ b{\isachardoublequote}}, for example. This involves the trivial rule
369 \isa{{\isachardoublequote}PROP\ {\isasympsi}\ {\isasymLongrightarrow}\ PROP\ {\isasympsi}{\isachardoublequote}}, which is bound in Isabelle/Pure as
370 ``\indexref{}{fact}{\_}\hyperlink{fact.underscore}{\mbox{\isa{{\isacharunderscore}}}}'' (underscore).
372 Automated methods (such as \hyperlink{method.simp}{\mbox{\isa{simp}}} or \hyperlink{method.auto}{\mbox{\isa{auto}}}) just
373 insert any given facts before their usual operation. Depending on
374 the kind of procedure involved, the order of facts is less
379 \isamarkupsubsection{Goals \label{sec:goals}%
383 \begin{isamarkuptext}%
384 \begin{matharray}{rcl}
385 \indexdef{}{command}{lemma}\hypertarget{command.lemma}{\hyperlink{command.lemma}{\mbox{\isa{\isacommand{lemma}}}}} & : & \isa{{\isachardoublequote}local{\isacharunderscore}theory\ {\isasymrightarrow}\ proof{\isacharparenleft}prove{\isacharparenright}{\isachardoublequote}} \\
386 \indexdef{}{command}{theorem}\hypertarget{command.theorem}{\hyperlink{command.theorem}{\mbox{\isa{\isacommand{theorem}}}}} & : & \isa{{\isachardoublequote}local{\isacharunderscore}theory\ {\isasymrightarrow}\ proof{\isacharparenleft}prove{\isacharparenright}{\isachardoublequote}} \\
387 \indexdef{}{command}{corollary}\hypertarget{command.corollary}{\hyperlink{command.corollary}{\mbox{\isa{\isacommand{corollary}}}}} & : & \isa{{\isachardoublequote}local{\isacharunderscore}theory\ {\isasymrightarrow}\ proof{\isacharparenleft}prove{\isacharparenright}{\isachardoublequote}} \\
388 \indexdef{}{command}{have}\hypertarget{command.have}{\hyperlink{command.have}{\mbox{\isa{\isacommand{have}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isacharbar}\ proof{\isacharparenleft}chain{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}prove{\isacharparenright}{\isachardoublequote}} \\
389 \indexdef{}{command}{show}\hypertarget{command.show}{\hyperlink{command.show}{\mbox{\isa{\isacommand{show}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isacharbar}\ proof{\isacharparenleft}chain{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}prove{\isacharparenright}{\isachardoublequote}} \\
390 \indexdef{}{command}{hence}\hypertarget{command.hence}{\hyperlink{command.hence}{\mbox{\isa{\isacommand{hence}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}prove{\isacharparenright}{\isachardoublequote}} \\
391 \indexdef{}{command}{thus}\hypertarget{command.thus}{\hyperlink{command.thus}{\mbox{\isa{\isacommand{thus}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}prove{\isacharparenright}{\isachardoublequote}} \\
392 \indexdef{}{command}{print\_statement}\hypertarget{command.print-statement}{\hyperlink{command.print-statement}{\mbox{\isa{\isacommand{print{\isacharunderscore}statement}}}}}\isa{{\isachardoublequote}\isactrlsup {\isacharasterisk}{\isachardoublequote}} & : & \isa{{\isachardoublequote}context\ {\isasymrightarrow}{\isachardoublequote}} \\
395 From a theory context, proof mode is entered by an initial goal
396 command such as \hyperlink{command.lemma}{\mbox{\isa{\isacommand{lemma}}}}, \hyperlink{command.theorem}{\mbox{\isa{\isacommand{theorem}}}}, or
397 \hyperlink{command.corollary}{\mbox{\isa{\isacommand{corollary}}}}. Within a proof, new claims may be
398 introduced locally as well; four variants are available here to
399 indicate whether forward chaining of facts should be performed
400 initially (via \indexref{}{command}{then}\hyperlink{command.then}{\mbox{\isa{\isacommand{then}}}}), and whether the final result
401 is meant to solve some pending goal.
403 Goals may consist of multiple statements, resulting in a list of
404 facts eventually. A pending multi-goal is internally represented as
405 a meta-level conjunction (\isa{{\isachardoublequote}{\isacharampersand}{\isacharampersand}{\isacharampersand}{\isachardoublequote}}), which is usually
406 split into the corresponding number of sub-goals prior to an initial
407 method application, via \indexref{}{command}{proof}\hyperlink{command.proof}{\mbox{\isa{\isacommand{proof}}}}
408 (\secref{sec:proof-steps}) or \indexref{}{command}{apply}\hyperlink{command.apply}{\mbox{\isa{\isacommand{apply}}}}
409 (\secref{sec:tactic-commands}). The \indexref{}{method}{induct}\hyperlink{method.induct}{\mbox{\isa{induct}}} method
410 covered in \secref{sec:cases-induct} acts on multiple claims
413 Claims at the theory level may be either in short or long form. A
414 short goal merely consists of several simultaneous propositions
415 (often just one). A long goal includes an explicit context
416 specification for the subsequent conclusion, involving local
417 parameters and assumptions. Here the role of each part of the
418 statement is explicitly marked by separate keywords (see also
419 \secref{sec:locale}); the local assumptions being introduced here
420 are available as \indexref{}{fact}{assms}\hyperlink{fact.assms}{\mbox{\isa{assms}}} in the proof. Moreover, there
421 are two kinds of conclusions: \indexdef{}{element}{shows}\hypertarget{element.shows}{\hyperlink{element.shows}{\mbox{\isa{\isakeyword{shows}}}}} states several
422 simultaneous propositions (essentially a big conjunction), while
423 \indexdef{}{element}{obtains}\hypertarget{element.obtains}{\hyperlink{element.obtains}{\mbox{\isa{\isakeyword{obtains}}}}} claims several simultaneous simultaneous
424 contexts of (essentially a big disjunction of eliminated parameters
425 and assumptions, cf.\ \secref{sec:obtain}).
428 ('lemma' | 'theorem' | 'corollary') target? (goal | longgoal)
430 ('have' | 'show' | 'hence' | 'thus') goal
432 'print\_statement' modes? thmrefs
435 goal: (props + 'and')
437 longgoal: thmdecl? (contextelem *) conclusion
439 conclusion: 'shows' goal | 'obtains' (parname? case + '|')
441 case: (vars + 'and') 'where' (props + 'and')
447 \item \hyperlink{command.lemma}{\mbox{\isa{\isacommand{lemma}}}}~\isa{{\isachardoublequote}a{\isacharcolon}\ {\isasymphi}{\isachardoublequote}} enters proof mode with
448 \isa{{\isasymphi}} as main goal, eventually resulting in some fact \isa{{\isachardoublequote}{\isasymturnstile}\ {\isasymphi}{\isachardoublequote}} to be put back into the target context. An additional
449 \railnonterm{context} specification may build up an initial proof
450 context for the subsequent claim; this includes local definitions
451 and syntax as well, see the definition of \hyperlink{syntax.contextelem}{\mbox{\isa{contextelem}}} in
454 \item \hyperlink{command.theorem}{\mbox{\isa{\isacommand{theorem}}}}~\isa{{\isachardoublequote}a{\isacharcolon}\ {\isasymphi}{\isachardoublequote}} and \hyperlink{command.corollary}{\mbox{\isa{\isacommand{corollary}}}}~\isa{{\isachardoublequote}a{\isacharcolon}\ {\isasymphi}{\isachardoublequote}} are essentially the same as \hyperlink{command.lemma}{\mbox{\isa{\isacommand{lemma}}}}~\isa{{\isachardoublequote}a{\isacharcolon}\ {\isasymphi}{\isachardoublequote}}, but the facts are internally marked as
455 being of a different kind. This discrimination acts like a formal
458 \item \hyperlink{command.have}{\mbox{\isa{\isacommand{have}}}}~\isa{{\isachardoublequote}a{\isacharcolon}\ {\isasymphi}{\isachardoublequote}} claims a local goal,
459 eventually resulting in a fact within the current logical context.
460 This operation is completely independent of any pending sub-goals of
461 an enclosing goal statements, so \hyperlink{command.have}{\mbox{\isa{\isacommand{have}}}} may be freely
462 used for experimental exploration of potential results within a
465 \item \hyperlink{command.show}{\mbox{\isa{\isacommand{show}}}}~\isa{{\isachardoublequote}a{\isacharcolon}\ {\isasymphi}{\isachardoublequote}} is like \hyperlink{command.have}{\mbox{\isa{\isacommand{have}}}}~\isa{{\isachardoublequote}a{\isacharcolon}\ {\isasymphi}{\isachardoublequote}} plus a second stage to refine some pending
466 sub-goal for each one of the finished result, after having been
467 exported into the corresponding context (at the head of the
468 sub-proof of this \hyperlink{command.show}{\mbox{\isa{\isacommand{show}}}} command).
470 To accommodate interactive debugging, resulting rules are printed
471 before being applied internally. Even more, interactive execution
472 of \hyperlink{command.show}{\mbox{\isa{\isacommand{show}}}} predicts potential failure and displays the
473 resulting error as a warning beforehand. Watch out for the
476 %FIXME proper antiquitation
478 Problem! Local statement will fail to solve any pending goal
481 \item \hyperlink{command.hence}{\mbox{\isa{\isacommand{hence}}}} abbreviates ``\hyperlink{command.then}{\mbox{\isa{\isacommand{then}}}}~\hyperlink{command.have}{\mbox{\isa{\isacommand{have}}}}'', i.e.\ claims a local goal to be proven by forward
482 chaining the current facts. Note that \hyperlink{command.hence}{\mbox{\isa{\isacommand{hence}}}} is also
483 equivalent to ``\hyperlink{command.from}{\mbox{\isa{\isacommand{from}}}}~\isa{this}~\hyperlink{command.have}{\mbox{\isa{\isacommand{have}}}}''.
485 \item \hyperlink{command.thus}{\mbox{\isa{\isacommand{thus}}}} abbreviates ``\hyperlink{command.then}{\mbox{\isa{\isacommand{then}}}}~\hyperlink{command.show}{\mbox{\isa{\isacommand{show}}}}''. Note that \hyperlink{command.thus}{\mbox{\isa{\isacommand{thus}}}} is also equivalent to
486 ``\hyperlink{command.from}{\mbox{\isa{\isacommand{from}}}}~\isa{this}~\hyperlink{command.show}{\mbox{\isa{\isacommand{show}}}}''.
488 \item \hyperlink{command.print-statement}{\mbox{\isa{\isacommand{print{\isacharunderscore}statement}}}}~\isa{a} prints facts from the
489 current theory or proof context in long statement form, according to
490 the syntax for \hyperlink{command.lemma}{\mbox{\isa{\isacommand{lemma}}}} given above.
494 Any goal statement causes some term abbreviations (such as
495 \indexref{}{variable}{?thesis}\hyperlink{variable.?thesis}{\mbox{\isa{{\isacharquery}thesis}}}) to be bound automatically, see also
496 \secref{sec:term-abbrev}.
498 The optional case names of \indexref{}{element}{obtains}\hyperlink{element.obtains}{\mbox{\isa{\isakeyword{obtains}}}} have a twofold
499 meaning: (1) during the of this claim they refer to the the local
500 context introductions, (2) the resulting rule is annotated
501 accordingly to support symbolic case splits when used with the
502 \indexref{}{method}{cases}\hyperlink{method.cases}{\mbox{\isa{cases}}} method (cf.\ \secref{sec:cases-induct}).
507 Isabelle/Isar suffers theory-level goal statements to contain
508 \emph{unbound schematic variables}, although this does not conform
509 to the aim of human-readable proof documents! The main problem
510 with schematic goals is that the actual outcome is usually hard to
511 predict, depending on the behavior of the proof methods applied
512 during the course of reasoning. Note that most semi-automated
513 methods heavily depend on several kinds of implicit rule
514 declarations within the current theory context. As this would
515 also result in non-compositional checking of sub-proofs,
516 \emph{local goals} are not allowed to be schematic at all.
517 Nevertheless, schematic goals do have their use in Prolog-style
518 interactive synthesis of proven results, usually by stepwise
519 refinement via emulation of traditional Isabelle tactic scripts
520 (see also \secref{sec:tactic-commands}). In any case, users
521 should know what they are doing.
526 \isamarkupsection{Refinement steps%
530 \isamarkupsubsection{Proof method expressions \label{sec:proof-meth}%
534 \begin{isamarkuptext}%
535 Proof methods are either basic ones, or expressions composed of
536 methods via ``\verb|,|'' (sequential composition),
537 ``\verb||\verb,|,\verb||'' (alternative choices), ``\verb|?|''
538 (try), ``\verb|+|'' (repeat at least once), ``\verb|[|\isa{n}\verb|]|'' (restriction to first \isa{n}
539 sub-goals, with default \isa{{\isachardoublequote}n\ {\isacharequal}\ {\isadigit{1}}{\isachardoublequote}}). In practice, proof
540 methods are usually just a comma separated list of
541 \railqtok{nameref}~\railnonterm{args} specifications. Note that
542 parentheses may be dropped for single method specifications (with no
545 \indexouternonterm{method}
547 method: (nameref | '(' methods ')') (() | '?' | '+' | '[' nat? ']')
549 methods: (nameref args | method) + (',' | '|')
553 Proper Isar proof methods do \emph{not} admit arbitrary goal
554 addressing, but refer either to the first sub-goal or all sub-goals
555 uniformly. The goal restriction operator ``\isa{{\isachardoublequote}{\isacharbrackleft}n{\isacharbrackright}{\isachardoublequote}}''
556 evaluates a method expression within a sandbox consisting of the
557 first \isa{n} sub-goals (which need to exist). For example, the
558 method ``\isa{{\isachardoublequote}simp{\isacharunderscore}all{\isacharbrackleft}{\isadigit{3}}{\isacharbrackright}{\isachardoublequote}}'' simplifies the first three
559 sub-goals, while ``\isa{{\isachardoublequote}{\isacharparenleft}rule\ foo{\isacharcomma}\ simp{\isacharunderscore}all{\isacharparenright}{\isacharbrackleft}{\isacharbrackright}{\isachardoublequote}}'' simplifies all
560 new goals that emerge from applying rule \isa{{\isachardoublequote}foo{\isachardoublequote}} to the
561 originally first one.
563 Improper methods, notably tactic emulations, offer a separate
564 low-level goal addressing scheme as explicit argument to the
565 individual tactic being involved. Here ``\isa{{\isachardoublequote}{\isacharbrackleft}{\isacharbang}{\isacharbrackright}{\isachardoublequote}}'' refers to
566 all goals, and ``\isa{{\isachardoublequote}{\isacharbrackleft}n{\isacharminus}{\isacharbrackright}{\isachardoublequote}}'' to all goals starting from \isa{{\isachardoublequote}n{\isachardoublequote}}.
568 \indexouternonterm{goalspec}
570 goalspec: '[' (nat '-' nat | nat '-' | nat | '!' ) ']'
576 \isamarkupsubsection{Initial and terminal proof steps \label{sec:proof-steps}%
580 \begin{isamarkuptext}%
581 \begin{matharray}{rcl}
582 \indexdef{}{command}{proof}\hypertarget{command.proof}{\hyperlink{command.proof}{\mbox{\isa{\isacommand{proof}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}prove{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}state{\isacharparenright}{\isachardoublequote}} \\
583 \indexdef{}{command}{qed}\hypertarget{command.qed}{\hyperlink{command.qed}{\mbox{\isa{\isacommand{qed}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}state{\isacharparenright}\ {\isacharbar}\ local{\isacharunderscore}theory\ {\isacharbar}\ theory{\isachardoublequote}} \\
584 \indexdef{}{command}{by}\hypertarget{command.by}{\hyperlink{command.by}{\mbox{\isa{\isacommand{by}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}prove{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}state{\isacharparenright}\ {\isacharbar}\ local{\isacharunderscore}theory\ {\isacharbar}\ theory{\isachardoublequote}} \\
585 \indexdef{}{command}{..}\hypertarget{command.ddot}{\hyperlink{command.ddot}{\mbox{\isa{\isacommand{{\isachardot}{\isachardot}}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}prove{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}state{\isacharparenright}\ {\isacharbar}\ local{\isacharunderscore}theory\ {\isacharbar}\ theory{\isachardoublequote}} \\
586 \indexdef{}{command}{.}\hypertarget{command.dot}{\hyperlink{command.dot}{\mbox{\isa{\isacommand{{\isachardot}}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}prove{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}state{\isacharparenright}\ {\isacharbar}\ local{\isacharunderscore}theory\ {\isacharbar}\ theory{\isachardoublequote}} \\
587 \indexdef{}{command}{sorry}\hypertarget{command.sorry}{\hyperlink{command.sorry}{\mbox{\isa{\isacommand{sorry}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}prove{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}state{\isacharparenright}\ {\isacharbar}\ local{\isacharunderscore}theory\ {\isacharbar}\ theory{\isachardoublequote}} \\
590 Arbitrary goal refinement via tactics is considered harmful.
591 Structured proof composition in Isar admits proof methods to be
592 invoked in two places only.
596 \item An \emph{initial} refinement step \indexref{}{command}{proof}\hyperlink{command.proof}{\mbox{\isa{\isacommand{proof}}}}~\isa{{\isachardoublequote}m\isactrlsub {\isadigit{1}}{\isachardoublequote}} reduces a newly stated goal to a number
597 of sub-goals that are to be solved later. Facts are passed to
598 \isa{{\isachardoublequote}m\isactrlsub {\isadigit{1}}{\isachardoublequote}} for forward chaining, if so indicated by \isa{{\isachardoublequote}proof{\isacharparenleft}chain{\isacharparenright}{\isachardoublequote}} mode.
600 \item A \emph{terminal} conclusion step \indexref{}{command}{qed}\hyperlink{command.qed}{\mbox{\isa{\isacommand{qed}}}}~\isa{{\isachardoublequote}m\isactrlsub {\isadigit{2}}{\isachardoublequote}} is intended to solve remaining goals. No facts are
601 passed to \isa{{\isachardoublequote}m\isactrlsub {\isadigit{2}}{\isachardoublequote}}.
605 The only other (proper) way to affect pending goals in a proof body
606 is by \indexref{}{command}{show}\hyperlink{command.show}{\mbox{\isa{\isacommand{show}}}}, which involves an explicit statement of
607 what is to be solved eventually. Thus we avoid the fundamental
608 problem of unstructured tactic scripts that consist of numerous
609 consecutive goal transformations, with invisible effects.
611 \medskip As a general rule of thumb for good proof style, initial
612 proof methods should either solve the goal completely, or constitute
613 some well-understood reduction to new sub-goals. Arbitrary
614 automatic proof tools that are prone leave a large number of badly
615 structured sub-goals are no help in continuing the proof document in
616 an intelligible manner.
618 Unless given explicitly by the user, the default initial method is
619 ``\indexref{}{method}{rule}\hyperlink{method.rule}{\mbox{\isa{rule}}}'', which applies a single standard elimination
620 or introduction rule according to the topmost symbol involved.
621 There is no separate default terminal method. Any remaining goals
622 are always solved by assumption in the very last step.
631 ('.' | '..' | 'sorry')
637 \item \hyperlink{command.proof}{\mbox{\isa{\isacommand{proof}}}}~\isa{{\isachardoublequote}m\isactrlsub {\isadigit{1}}{\isachardoublequote}} refines the goal by proof
638 method \isa{{\isachardoublequote}m\isactrlsub {\isadigit{1}}{\isachardoublequote}}; facts for forward chaining are passed if so
639 indicated by \isa{{\isachardoublequote}proof{\isacharparenleft}chain{\isacharparenright}{\isachardoublequote}} mode.
641 \item \hyperlink{command.qed}{\mbox{\isa{\isacommand{qed}}}}~\isa{{\isachardoublequote}m\isactrlsub {\isadigit{2}}{\isachardoublequote}} refines any remaining goals by
642 proof method \isa{{\isachardoublequote}m\isactrlsub {\isadigit{2}}{\isachardoublequote}} and concludes the sub-proof by assumption.
643 If the goal had been \isa{{\isachardoublequote}show{\isachardoublequote}} (or \isa{{\isachardoublequote}thus{\isachardoublequote}}), some
644 pending sub-goal is solved as well by the rule resulting from the
645 result \emph{exported} into the enclosing goal context. Thus \isa{{\isachardoublequote}qed{\isachardoublequote}} may fail for two reasons: either \isa{{\isachardoublequote}m\isactrlsub {\isadigit{2}}{\isachardoublequote}} fails, or the
646 resulting rule does not fit to any pending goal\footnote{This
647 includes any additional ``strong'' assumptions as introduced by
648 \hyperlink{command.assume}{\mbox{\isa{\isacommand{assume}}}}.} of the enclosing context. Debugging such a
649 situation might involve temporarily changing \hyperlink{command.show}{\mbox{\isa{\isacommand{show}}}} into
650 \hyperlink{command.have}{\mbox{\isa{\isacommand{have}}}}, or weakening the local context by replacing
651 occurrences of \hyperlink{command.assume}{\mbox{\isa{\isacommand{assume}}}} by \hyperlink{command.presume}{\mbox{\isa{\isacommand{presume}}}}.
653 \item \hyperlink{command.by}{\mbox{\isa{\isacommand{by}}}}~\isa{{\isachardoublequote}m\isactrlsub {\isadigit{1}}\ m\isactrlsub {\isadigit{2}}{\isachardoublequote}} is a \emph{terminal
654 proof}\index{proof!terminal}; it abbreviates \hyperlink{command.proof}{\mbox{\isa{\isacommand{proof}}}}~\isa{{\isachardoublequote}m\isactrlsub {\isadigit{1}}{\isachardoublequote}}~\isa{{\isachardoublequote}qed{\isachardoublequote}}~\isa{{\isachardoublequote}m\isactrlsub {\isadigit{2}}{\isachardoublequote}}, but with
655 backtracking across both methods. Debugging an unsuccessful
656 \hyperlink{command.by}{\mbox{\isa{\isacommand{by}}}}~\isa{{\isachardoublequote}m\isactrlsub {\isadigit{1}}\ m\isactrlsub {\isadigit{2}}{\isachardoublequote}} command can be done by expanding its
657 definition; in many cases \hyperlink{command.proof}{\mbox{\isa{\isacommand{proof}}}}~\isa{{\isachardoublequote}m\isactrlsub {\isadigit{1}}{\isachardoublequote}} (or even
658 \isa{{\isachardoublequote}apply{\isachardoublequote}}~\isa{{\isachardoublequote}m\isactrlsub {\isadigit{1}}{\isachardoublequote}}) is already sufficient to see the
661 \item ``\hyperlink{command.ddot}{\mbox{\isa{\isacommand{{\isachardot}{\isachardot}}}}}'' is a \emph{default
662 proof}\index{proof!default}; it abbreviates \hyperlink{command.by}{\mbox{\isa{\isacommand{by}}}}~\isa{{\isachardoublequote}rule{\isachardoublequote}}.
664 \item ``\hyperlink{command.dot}{\mbox{\isa{\isacommand{{\isachardot}}}}}'' is a \emph{trivial
665 proof}\index{proof!trivial}; it abbreviates \hyperlink{command.by}{\mbox{\isa{\isacommand{by}}}}~\isa{{\isachardoublequote}this{\isachardoublequote}}.
667 \item \hyperlink{command.sorry}{\mbox{\isa{\isacommand{sorry}}}} is a \emph{fake proof}\index{proof!fake}
668 pretending to solve the pending claim without further ado. This
669 only works in interactive development, or if the \verb|quick_and_dirty| flag is enabled (in ML). Facts emerging from fake
670 proofs are not the real thing. Internally, each theorem container
671 is tainted by an oracle invocation, which is indicated as ``\isa{{\isachardoublequote}{\isacharbrackleft}{\isacharbang}{\isacharbrackright}{\isachardoublequote}}'' in the printed result.
673 The most important application of \hyperlink{command.sorry}{\mbox{\isa{\isacommand{sorry}}}} is to support
674 experimentation and top-down proof development.
680 \isamarkupsubsection{Fundamental methods and attributes \label{sec:pure-meth-att}%
684 \begin{isamarkuptext}%
685 The following proof methods and attributes refer to basic logical
686 operations of Isar. Further methods and attributes are provided by
687 several generic and object-logic specific tools and packages (see
688 \chref{ch:gen-tools} and \chref{ch:hol}).
690 \begin{matharray}{rcl}
691 \indexdef{}{method}{-}\hypertarget{method.-}{\hyperlink{method.-}{\mbox{\isa{{\isacharminus}}}}} & : & \isa{method} \\
692 \indexdef{}{method}{fact}\hypertarget{method.fact}{\hyperlink{method.fact}{\mbox{\isa{fact}}}} & : & \isa{method} \\
693 \indexdef{}{method}{assumption}\hypertarget{method.assumption}{\hyperlink{method.assumption}{\mbox{\isa{assumption}}}} & : & \isa{method} \\
694 \indexdef{}{method}{this}\hypertarget{method.this}{\hyperlink{method.this}{\mbox{\isa{this}}}} & : & \isa{method} \\
695 \indexdef{}{method}{rule}\hypertarget{method.rule}{\hyperlink{method.rule}{\mbox{\isa{rule}}}} & : & \isa{method} \\
696 \indexdef{}{method}{iprover}\hypertarget{method.iprover}{\hyperlink{method.iprover}{\mbox{\isa{iprover}}}} & : & \isa{method} \\[0.5ex]
697 \indexdef{Pure}{attribute}{intro}\hypertarget{attribute.Pure.intro}{\hyperlink{attribute.Pure.intro}{\mbox{\isa{intro}}}} & : & \isa{attribute} \\
698 \indexdef{Pure}{attribute}{elim}\hypertarget{attribute.Pure.elim}{\hyperlink{attribute.Pure.elim}{\mbox{\isa{elim}}}} & : & \isa{attribute} \\
699 \indexdef{Pure}{attribute}{dest}\hypertarget{attribute.Pure.dest}{\hyperlink{attribute.Pure.dest}{\mbox{\isa{dest}}}} & : & \isa{attribute} \\
700 \indexdef{}{attribute}{rule}\hypertarget{attribute.rule}{\hyperlink{attribute.rule}{\mbox{\isa{rule}}}} & : & \isa{attribute} \\[0.5ex]
701 \indexdef{}{attribute}{OF}\hypertarget{attribute.OF}{\hyperlink{attribute.OF}{\mbox{\isa{OF}}}} & : & \isa{attribute} \\
702 \indexdef{}{attribute}{of}\hypertarget{attribute.of}{\hyperlink{attribute.of}{\mbox{\isa{of}}}} & : & \isa{attribute} \\
703 \indexdef{}{attribute}{where}\hypertarget{attribute.where}{\hyperlink{attribute.where}{\mbox{\isa{where}}}} & : & \isa{attribute} \\
711 'iprover' ('!' ?) (rulemod *)
713 rulemod: ('intro' | 'elim' | 'dest') ((('!' | () | '?') nat?) | 'del') ':' thmrefs
715 ('intro' | 'elim' | 'dest') ('!' | () | '?') nat?
721 'of' insts ('concl' ':' insts)?
723 'where' ((name | var | typefree | typevar) '=' (type | term) * 'and')
729 \item ``\hyperlink{method.-}{\mbox{\isa{{\isacharminus}}}}'' (minus) does nothing but insert the forward
730 chaining facts as premises into the goal. Note that command
731 \indexref{}{command}{proof}\hyperlink{command.proof}{\mbox{\isa{\isacommand{proof}}}} without any method actually performs a single
732 reduction step using the \indexref{}{method}{rule}\hyperlink{method.rule}{\mbox{\isa{rule}}} method; thus a plain
733 \emph{do-nothing} proof step would be ``\hyperlink{command.proof}{\mbox{\isa{\isacommand{proof}}}}~\isa{{\isachardoublequote}{\isacharminus}{\isachardoublequote}}'' rather than \hyperlink{command.proof}{\mbox{\isa{\isacommand{proof}}}} alone.
735 \item \hyperlink{method.fact}{\mbox{\isa{fact}}}~\isa{{\isachardoublequote}a\isactrlsub {\isadigit{1}}\ {\isasymdots}\ a\isactrlsub n{\isachardoublequote}} composes some fact from
736 \isa{{\isachardoublequote}a\isactrlsub {\isadigit{1}}{\isacharcomma}\ {\isasymdots}{\isacharcomma}\ a\isactrlsub n{\isachardoublequote}} (or implicitly from the current proof context)
737 modulo unification of schematic type and term variables. The rule
738 structure is not taken into account, i.e.\ meta-level implication is
739 considered atomic. This is the same principle underlying literal
740 facts (cf.\ \secref{sec:syn-att}): ``\hyperlink{command.have}{\mbox{\isa{\isacommand{have}}}}~\isa{{\isachardoublequote}{\isasymphi}{\isachardoublequote}}~\hyperlink{command.by}{\mbox{\isa{\isacommand{by}}}}~\isa{fact}'' is equivalent to ``\hyperlink{command.note}{\mbox{\isa{\isacommand{note}}}}~\verb|`|\isa{{\isasymphi}}\verb|`|'' provided that
741 \isa{{\isachardoublequote}{\isasymturnstile}\ {\isasymphi}{\isachardoublequote}} is an instance of some known \isa{{\isachardoublequote}{\isasymturnstile}\ {\isasymphi}{\isachardoublequote}} in the
744 \item \hyperlink{method.assumption}{\mbox{\isa{assumption}}} solves some goal by a single assumption
745 step. All given facts are guaranteed to participate in the
746 refinement; this means there may be only 0 or 1 in the first place.
747 Recall that \hyperlink{command.qed}{\mbox{\isa{\isacommand{qed}}}} (\secref{sec:proof-steps}) already
748 concludes any remaining sub-goals by assumption, so structured
749 proofs usually need not quote the \hyperlink{method.assumption}{\mbox{\isa{assumption}}} method at
752 \item \hyperlink{method.this}{\mbox{\isa{this}}} applies all of the current facts directly as
753 rules. Recall that ``\hyperlink{command.dot}{\mbox{\isa{\isacommand{{\isachardot}}}}}'' (dot) abbreviates ``\hyperlink{command.by}{\mbox{\isa{\isacommand{by}}}}~\isa{this}''.
755 \item \hyperlink{method.rule}{\mbox{\isa{rule}}}~\isa{{\isachardoublequote}a\isactrlsub {\isadigit{1}}\ {\isasymdots}\ a\isactrlsub n{\isachardoublequote}} applies some rule given as
756 argument in backward manner; facts are used to reduce the rule
757 before applying it to the goal. Thus \hyperlink{method.rule}{\mbox{\isa{rule}}} without facts
758 is plain introduction, while with facts it becomes elimination.
760 When no arguments are given, the \hyperlink{method.rule}{\mbox{\isa{rule}}} method tries to pick
761 appropriate rules automatically, as declared in the current context
762 using the \hyperlink{attribute.Pure.intro}{\mbox{\isa{intro}}}, \hyperlink{attribute.Pure.elim}{\mbox{\isa{elim}}},
763 \hyperlink{attribute.Pure.dest}{\mbox{\isa{dest}}} attributes (see below). This is the
764 default behavior of \hyperlink{command.proof}{\mbox{\isa{\isacommand{proof}}}} and ``\hyperlink{command.ddot}{\mbox{\isa{\isacommand{{\isachardot}{\isachardot}}}}}''
765 (double-dot) steps (see \secref{sec:proof-steps}).
767 \item \hyperlink{method.iprover}{\mbox{\isa{iprover}}} performs intuitionistic proof search,
768 depending on specifically declared rules from the context, or given
769 as explicit arguments. Chained facts are inserted into the goal
770 before commencing proof search; ``\hyperlink{method.iprover}{\mbox{\isa{iprover}}}\isa{{\isachardoublequote}{\isacharbang}{\isachardoublequote}}''
771 means to include the current \hyperlink{fact.prems}{\mbox{\isa{prems}}} as well.
773 Rules need to be classified as \hyperlink{attribute.Pure.intro}{\mbox{\isa{intro}}},
774 \hyperlink{attribute.Pure.elim}{\mbox{\isa{elim}}}, or \hyperlink{attribute.Pure.dest}{\mbox{\isa{dest}}}; here the
775 ``\isa{{\isachardoublequote}{\isacharbang}{\isachardoublequote}}'' indicator refers to ``safe'' rules, which may be
776 applied aggressively (without considering back-tracking later).
777 Rules declared with ``\isa{{\isachardoublequote}{\isacharquery}{\isachardoublequote}}'' are ignored in proof search (the
778 single-step \hyperlink{method.rule}{\mbox{\isa{rule}}} method still observes these). An
779 explicit weight annotation may be given as well; otherwise the
780 number of rule premises will be taken into account here.
782 \item \hyperlink{attribute.Pure.intro}{\mbox{\isa{intro}}}, \hyperlink{attribute.Pure.elim}{\mbox{\isa{elim}}}, and
783 \hyperlink{attribute.Pure.dest}{\mbox{\isa{dest}}} declare introduction, elimination, and
784 destruct rules, to be used with the \hyperlink{method.rule}{\mbox{\isa{rule}}} and \hyperlink{method.iprover}{\mbox{\isa{iprover}}} methods. Note that the latter will ignore rules declared
785 with ``\isa{{\isachardoublequote}{\isacharquery}{\isachardoublequote}}'', while ``\isa{{\isachardoublequote}{\isacharbang}{\isachardoublequote}}'' are used most
788 The classical reasoner (see \secref{sec:classical}) introduces its
789 own variants of these attributes; use qualified names to access the
790 present versions of Isabelle/Pure, i.e.\ \hyperlink{attribute.Pure.Pure.intro}{\mbox{\isa{Pure{\isachardot}intro}}}.
792 \item \hyperlink{attribute.rule}{\mbox{\isa{rule}}}~\isa{del} undeclares introduction,
793 elimination, or destruct rules.
795 \item \hyperlink{attribute.OF}{\mbox{\isa{OF}}}~\isa{{\isachardoublequote}a\isactrlsub {\isadigit{1}}\ {\isasymdots}\ a\isactrlsub n{\isachardoublequote}} applies some theorem to all
796 of the given rules \isa{{\isachardoublequote}a\isactrlsub {\isadigit{1}}{\isacharcomma}\ {\isasymdots}{\isacharcomma}\ a\isactrlsub n{\isachardoublequote}} (in parallel). This
797 corresponds to the \verb|op MRS| operation in ML,
798 but note the reversed order. Positions may be effectively skipped
799 by including ``\isa{{\isacharunderscore}}'' (underscore) as argument.
801 \item \hyperlink{attribute.of}{\mbox{\isa{of}}}~\isa{{\isachardoublequote}t\isactrlsub {\isadigit{1}}\ {\isasymdots}\ t\isactrlsub n{\isachardoublequote}} performs positional
802 instantiation of term variables. The terms \isa{{\isachardoublequote}t\isactrlsub {\isadigit{1}}{\isacharcomma}\ {\isasymdots}{\isacharcomma}\ t\isactrlsub n{\isachardoublequote}} are
803 substituted for any schematic variables occurring in a theorem from
804 left to right; ``\isa{{\isacharunderscore}}'' (underscore) indicates to skip a
805 position. Arguments following a ``\isa{{\isachardoublequote}concl{\isacharcolon}{\isachardoublequote}}'' specification
806 refer to positions of the conclusion of a rule.
808 \item \hyperlink{attribute.where}{\mbox{\isa{where}}}~\isa{{\isachardoublequote}x\isactrlsub {\isadigit{1}}\ {\isacharequal}\ t\isactrlsub {\isadigit{1}}\ {\isasymAND}\ {\isasymdots}\ x\isactrlsub n\ {\isacharequal}\ t\isactrlsub n{\isachardoublequote}}
809 performs named instantiation of schematic type and term variables
810 occurring in a theorem. Schematic variables have to be specified on
811 the left-hand side (e.g.\ \isa{{\isachardoublequote}{\isacharquery}x{\isadigit{1}}{\isachardot}{\isadigit{3}}{\isachardoublequote}}). The question mark may
812 be omitted if the variable name is a plain identifier without index.
813 As type instantiations are inferred from term instantiations,
814 explicit type instantiations are seldom necessary.
820 \isamarkupsubsection{Emulating tactic scripts \label{sec:tactic-commands}%
824 \begin{isamarkuptext}%
825 The Isar provides separate commands to accommodate tactic-style
826 proof scripts within the same system. While being outside the
827 orthodox Isar proof language, these might come in handy for
828 interactive exploration and debugging, or even actual tactical proof
829 within new-style theories (to benefit from document preparation, for
830 example). See also \secref{sec:tactics} for actual tactics, that
831 have been encapsulated as proof methods. Proper proof methods may
832 be used in scripts, too.
834 \begin{matharray}{rcl}
835 \indexdef{}{command}{apply}\hypertarget{command.apply}{\hyperlink{command.apply}{\mbox{\isa{\isacommand{apply}}}}}\isa{{\isachardoublequote}\isactrlsup {\isacharasterisk}{\isachardoublequote}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}prove{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}prove{\isacharparenright}{\isachardoublequote}} \\
836 \indexdef{}{command}{apply\_end}\hypertarget{command.apply-end}{\hyperlink{command.apply-end}{\mbox{\isa{\isacommand{apply{\isacharunderscore}end}}}}}\isa{{\isachardoublequote}\isactrlsup {\isacharasterisk}{\isachardoublequote}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}state{\isacharparenright}{\isachardoublequote}} \\
837 \indexdef{}{command}{done}\hypertarget{command.done}{\hyperlink{command.done}{\mbox{\isa{\isacommand{done}}}}}\isa{{\isachardoublequote}\isactrlsup {\isacharasterisk}{\isachardoublequote}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}prove{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}state{\isacharparenright}\ {\isacharbar}\ local{\isacharunderscore}theory\ {\isacharbar}\ theory{\isachardoublequote}} \\
838 \indexdef{}{command}{defer}\hypertarget{command.defer}{\hyperlink{command.defer}{\mbox{\isa{\isacommand{defer}}}}}\isa{{\isachardoublequote}\isactrlsup {\isacharasterisk}{\isachardoublequote}} & : & \isa{{\isachardoublequote}proof\ {\isasymrightarrow}\ proof{\isachardoublequote}} \\
839 \indexdef{}{command}{prefer}\hypertarget{command.prefer}{\hyperlink{command.prefer}{\mbox{\isa{\isacommand{prefer}}}}}\isa{{\isachardoublequote}\isactrlsup {\isacharasterisk}{\isachardoublequote}} & : & \isa{{\isachardoublequote}proof\ {\isasymrightarrow}\ proof{\isachardoublequote}} \\
840 \indexdef{}{command}{back}\hypertarget{command.back}{\hyperlink{command.back}{\mbox{\isa{\isacommand{back}}}}}\isa{{\isachardoublequote}\isactrlsup {\isacharasterisk}{\isachardoublequote}} & : & \isa{{\isachardoublequote}proof\ {\isasymrightarrow}\ proof{\isachardoublequote}} \\
844 ( 'apply' | 'apply\_end' ) method
854 \item \hyperlink{command.apply}{\mbox{\isa{\isacommand{apply}}}}~\isa{m} applies proof method \isa{m} in
855 initial position, but unlike \hyperlink{command.proof}{\mbox{\isa{\isacommand{proof}}}} it retains ``\isa{{\isachardoublequote}proof{\isacharparenleft}prove{\isacharparenright}{\isachardoublequote}}'' mode. Thus consecutive method applications may be
856 given just as in tactic scripts.
858 Facts are passed to \isa{m} as indicated by the goal's
859 forward-chain mode, and are \emph{consumed} afterwards. Thus any
860 further \hyperlink{command.apply}{\mbox{\isa{\isacommand{apply}}}} command would always work in a purely
863 \item \hyperlink{command.apply-end}{\mbox{\isa{\isacommand{apply{\isacharunderscore}end}}}}~\isa{{\isachardoublequote}m{\isachardoublequote}} applies proof method \isa{m} as if in terminal position. Basically, this simulates a
864 multi-step tactic script for \hyperlink{command.qed}{\mbox{\isa{\isacommand{qed}}}}, but may be given
865 anywhere within the proof body.
867 No facts are passed to \isa{m} here. Furthermore, the static
868 context is that of the enclosing goal (as for actual \hyperlink{command.qed}{\mbox{\isa{\isacommand{qed}}}}). Thus the proof method may not refer to any assumptions
869 introduced in the current body, for example.
871 \item \hyperlink{command.done}{\mbox{\isa{\isacommand{done}}}} completes a proof script, provided that the
872 current goal state is solved completely. Note that actual
873 structured proof commands (e.g.\ ``\hyperlink{command.dot}{\mbox{\isa{\isacommand{{\isachardot}}}}}'' or \hyperlink{command.sorry}{\mbox{\isa{\isacommand{sorry}}}}) may be used to conclude proof scripts as well.
875 \item \hyperlink{command.defer}{\mbox{\isa{\isacommand{defer}}}}~\isa{n} and \hyperlink{command.prefer}{\mbox{\isa{\isacommand{prefer}}}}~\isa{n}
876 shuffle the list of pending goals: \hyperlink{command.defer}{\mbox{\isa{\isacommand{defer}}}} puts off
877 sub-goal \isa{n} to the end of the list (\isa{{\isachardoublequote}n\ {\isacharequal}\ {\isadigit{1}}{\isachardoublequote}} by
878 default), while \hyperlink{command.prefer}{\mbox{\isa{\isacommand{prefer}}}} brings sub-goal \isa{n} to the
881 \item \hyperlink{command.back}{\mbox{\isa{\isacommand{back}}}} does back-tracking over the result sequence
882 of the latest proof command. Basically, any proof command may
883 return multiple results.
887 Any proper Isar proof method may be used with tactic script commands
888 such as \hyperlink{command.apply}{\mbox{\isa{\isacommand{apply}}}}. A few additional emulations of actual
889 tactics are provided as well; these would be never used in actual
890 structured proofs, of course.%
894 \isamarkupsubsection{Defining proof methods%
898 \begin{isamarkuptext}%
899 \begin{matharray}{rcl}
900 \indexdef{}{command}{method\_setup}\hypertarget{command.method-setup}{\hyperlink{command.method-setup}{\mbox{\isa{\isacommand{method{\isacharunderscore}setup}}}}} & : & \isa{{\isachardoublequote}theory\ {\isasymrightarrow}\ theory{\isachardoublequote}} \\
904 'method\_setup' name '=' text text
910 \item \hyperlink{command.method-setup}{\mbox{\isa{\isacommand{method{\isacharunderscore}setup}}}}~\isa{{\isachardoublequote}name\ {\isacharequal}\ text\ description{\isachardoublequote}}
911 defines a proof method in the current theory. The given \isa{{\isachardoublequote}text{\isachardoublequote}} has to be an ML expression of type \verb|Args.src -> Proof.context -> Proof.method|. Parsing concrete
912 method syntax from \verb|Args.src| input can be quite tedious in
913 general. The following simple examples are for methods without any
914 explicit arguments, or a list of theorems, respectively.
916 %FIXME proper antiquotations
919 Method.no_args (Method.METHOD (fn facts => foobar_tac))
920 Method.thms_args (fn thms => Method.METHOD (fn facts => foobar_tac))
921 Method.ctxt_args (fn ctxt => Method.METHOD (fn facts => foobar_tac))
922 Method.thms_ctxt_args (fn thms => fn ctxt =>
923 Method.METHOD (fn facts => foobar_tac))
927 Note that mere tactic emulations may ignore the \isa{facts}
928 parameter above. Proper proof methods would do something
929 appropriate with the list of current facts, though. Single-rule
930 methods usually do strict forward-chaining (e.g.\ by using \verb|Drule.multi_resolves|), while automatic ones just insert the facts
931 using \verb|Method.insert_tac| before applying the main tactic.
937 \isamarkupsection{Generalized elimination \label{sec:obtain}%
941 \begin{isamarkuptext}%
942 \begin{matharray}{rcl}
943 \indexdef{}{command}{obtain}\hypertarget{command.obtain}{\hyperlink{command.obtain}{\mbox{\isa{\isacommand{obtain}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isacharbar}\ proof{\isacharparenleft}chain{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}prove{\isacharparenright}{\isachardoublequote}} \\
944 \indexdef{}{command}{guess}\hypertarget{command.guess}{\hyperlink{command.guess}{\mbox{\isa{\isacommand{guess}}}}}\isa{{\isachardoublequote}\isactrlsup {\isacharasterisk}{\isachardoublequote}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isacharbar}\ proof{\isacharparenleft}chain{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}prove{\isacharparenright}{\isachardoublequote}} \\
947 Generalized elimination means that additional elements with certain
948 properties may be introduced in the current context, by virtue of a
949 locally proven ``soundness statement''. Technically speaking, the
950 \hyperlink{command.obtain}{\mbox{\isa{\isacommand{obtain}}}} language element is like a declaration of
951 \hyperlink{command.fix}{\mbox{\isa{\isacommand{fix}}}} and \hyperlink{command.assume}{\mbox{\isa{\isacommand{assume}}}} (see also see
952 \secref{sec:proof-context}), together with a soundness proof of its
953 additional claim. According to the nature of existential reasoning,
954 assumptions get eliminated from any result exported from the context
955 later, provided that the corresponding parameters do \emph{not}
956 occur in the conclusion.
959 'obtain' parname? (vars + 'and') 'where' (props + 'and')
961 'guess' (vars + 'and')
965 The derived Isar command \hyperlink{command.obtain}{\mbox{\isa{\isacommand{obtain}}}} is defined as follows
966 (where \isa{{\isachardoublequote}b\isactrlsub {\isadigit{1}}{\isacharcomma}\ {\isasymdots}{\isacharcomma}\ b\isactrlsub k{\isachardoublequote}} shall refer to (optional)
967 facts indicated for forward chaining).
969 \isa{{\isachardoublequote}{\isasymlangle}using\ b\isactrlsub {\isadigit{1}}\ {\isasymdots}\ b\isactrlsub k{\isasymrangle}{\isachardoublequote}}~~\hyperlink{command.obtain}{\mbox{\isa{\isacommand{obtain}}}}~\isa{{\isachardoublequote}x\isactrlsub {\isadigit{1}}\ {\isasymdots}\ x\isactrlsub m\ {\isasymWHERE}\ a{\isacharcolon}\ {\isasymphi}\isactrlsub {\isadigit{1}}\ {\isasymdots}\ {\isasymphi}\isactrlsub n\ \ {\isasymlangle}proof{\isasymrangle}\ {\isasymequiv}{\isachardoublequote}} \\[1ex]
970 \quad \hyperlink{command.have}{\mbox{\isa{\isacommand{have}}}}~\isa{{\isachardoublequote}{\isasymAnd}thesis{\isachardot}\ {\isacharparenleft}{\isasymAnd}x\isactrlsub {\isadigit{1}}\ {\isasymdots}\ x\isactrlsub m{\isachardot}\ {\isasymphi}\isactrlsub {\isadigit{1}}\ {\isasymLongrightarrow}\ {\isasymdots}\ {\isasymphi}\isactrlsub n\ {\isasymLongrightarrow}\ thesis{\isacharparenright}\ {\isasymLongrightarrow}\ thesis{\isachardoublequote}} \\
971 \quad \hyperlink{command.proof}{\mbox{\isa{\isacommand{proof}}}}~\hyperlink{method.succeed}{\mbox{\isa{succeed}}} \\
972 \qquad \hyperlink{command.fix}{\mbox{\isa{\isacommand{fix}}}}~\isa{thesis} \\
973 \qquad \hyperlink{command.assume}{\mbox{\isa{\isacommand{assume}}}}~\isa{{\isachardoublequote}that\ {\isacharbrackleft}Pure{\isachardot}intro{\isacharquery}{\isacharbrackright}{\isacharcolon}\ {\isasymAnd}x\isactrlsub {\isadigit{1}}\ {\isasymdots}\ x\isactrlsub m{\isachardot}\ {\isasymphi}\isactrlsub {\isadigit{1}}\ {\isasymLongrightarrow}\ {\isasymdots}\ {\isasymphi}\isactrlsub n\ {\isasymLongrightarrow}\ thesis{\isachardoublequote}} \\
974 \qquad \hyperlink{command.then}{\mbox{\isa{\isacommand{then}}}}~\hyperlink{command.show}{\mbox{\isa{\isacommand{show}}}}~\isa{thesis} \\
975 \quad\qquad \hyperlink{command.apply}{\mbox{\isa{\isacommand{apply}}}}~\isa{{\isacharminus}} \\
976 \quad\qquad \hyperlink{command.using}{\mbox{\isa{\isacommand{using}}}}~\isa{{\isachardoublequote}b\isactrlsub {\isadigit{1}}\ {\isasymdots}\ b\isactrlsub k\ \ {\isasymlangle}proof{\isasymrangle}{\isachardoublequote}} \\
977 \quad \hyperlink{command.qed}{\mbox{\isa{\isacommand{qed}}}} \\
978 \quad \hyperlink{command.fix}{\mbox{\isa{\isacommand{fix}}}}~\isa{{\isachardoublequote}x\isactrlsub {\isadigit{1}}\ {\isasymdots}\ x\isactrlsub m{\isachardoublequote}}~\hyperlink{command.assume}{\mbox{\isa{\isacommand{assume}}}}\isa{{\isachardoublequote}\isactrlsup {\isacharasterisk}\ a{\isacharcolon}\ {\isasymphi}\isactrlsub {\isadigit{1}}\ {\isasymdots}\ {\isasymphi}\isactrlsub n{\isachardoublequote}} \\
981 Typically, the soundness proof is relatively straight-forward, often
982 just by canonical automated tools such as ``\hyperlink{command.by}{\mbox{\isa{\isacommand{by}}}}~\isa{simp}'' or ``\hyperlink{command.by}{\mbox{\isa{\isacommand{by}}}}~\isa{blast}''. Accordingly, the
983 ``\isa{that}'' reduction above is declared as simplification and
986 In a sense, \hyperlink{command.obtain}{\mbox{\isa{\isacommand{obtain}}}} represents at the level of Isar
987 proofs what would be meta-logical existential quantifiers and
988 conjunctions. This concept has a broad range of useful
989 applications, ranging from plain elimination (or introduction) of
990 object-level existential and conjunctions, to elimination over
991 results of symbolic evaluation of recursive definitions, for
992 example. Also note that \hyperlink{command.obtain}{\mbox{\isa{\isacommand{obtain}}}} without parameters acts
993 much like \hyperlink{command.have}{\mbox{\isa{\isacommand{have}}}}, where the result is treated as a
996 An alternative name to be used instead of ``\isa{that}'' above may
997 be given in parentheses.
999 \medskip The improper variant \hyperlink{command.guess}{\mbox{\isa{\isacommand{guess}}}} is similar to
1000 \hyperlink{command.obtain}{\mbox{\isa{\isacommand{obtain}}}}, but derives the obtained statement from the
1001 course of reasoning! The proof starts with a fixed goal \isa{thesis}. The subsequent proof may refine this to anything of the
1002 form like \isa{{\isachardoublequote}{\isasymAnd}x\isactrlsub {\isadigit{1}}\ {\isasymdots}\ x\isactrlsub m{\isachardot}\ {\isasymphi}\isactrlsub {\isadigit{1}}\ {\isasymLongrightarrow}\ {\isasymdots}\ {\isasymphi}\isactrlsub n\ {\isasymLongrightarrow}\ thesis{\isachardoublequote}}, but must not introduce new subgoals. The
1003 final goal state is then used as reduction rule for the obtain
1004 scheme described above. Obtained parameters \isa{{\isachardoublequote}x\isactrlsub {\isadigit{1}}{\isacharcomma}\ {\isasymdots}{\isacharcomma}\ x\isactrlsub m{\isachardoublequote}} are marked as internal by default, which prevents the
1005 proof context from being polluted by ad-hoc variables. The variable
1006 names and type constraints given as arguments for \hyperlink{command.guess}{\mbox{\isa{\isacommand{guess}}}}
1007 specify a prefix of obtained parameters explicitly in the text.
1009 It is important to note that the facts introduced by \hyperlink{command.obtain}{\mbox{\isa{\isacommand{obtain}}}} and \hyperlink{command.guess}{\mbox{\isa{\isacommand{guess}}}} may not be polymorphic: any
1010 type-variables occurring here are fixed in the present context!%
1011 \end{isamarkuptext}%
1014 \isamarkupsection{Calculational reasoning \label{sec:calculation}%
1018 \begin{isamarkuptext}%
1019 \begin{matharray}{rcl}
1020 \indexdef{}{command}{also}\hypertarget{command.also}{\hyperlink{command.also}{\mbox{\isa{\isacommand{also}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}state{\isacharparenright}{\isachardoublequote}} \\
1021 \indexdef{}{command}{finally}\hypertarget{command.finally}{\hyperlink{command.finally}{\mbox{\isa{\isacommand{finally}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}chain{\isacharparenright}{\isachardoublequote}} \\
1022 \indexdef{}{command}{moreover}\hypertarget{command.moreover}{\hyperlink{command.moreover}{\mbox{\isa{\isacommand{moreover}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}state{\isacharparenright}{\isachardoublequote}} \\
1023 \indexdef{}{command}{ultimately}\hypertarget{command.ultimately}{\hyperlink{command.ultimately}{\mbox{\isa{\isacommand{ultimately}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}chain{\isacharparenright}{\isachardoublequote}} \\
1024 \indexdef{}{command}{print\_trans\_rules}\hypertarget{command.print-trans-rules}{\hyperlink{command.print-trans-rules}{\mbox{\isa{\isacommand{print{\isacharunderscore}trans{\isacharunderscore}rules}}}}}\isa{{\isachardoublequote}\isactrlsup {\isacharasterisk}{\isachardoublequote}} & : & \isa{{\isachardoublequote}context\ {\isasymrightarrow}{\isachardoublequote}} \\
1025 \hyperlink{attribute.trans}{\mbox{\isa{trans}}} & : & \isa{attribute} \\
1026 \hyperlink{attribute.sym}{\mbox{\isa{sym}}} & : & \isa{attribute} \\
1027 \hyperlink{attribute.symmetric}{\mbox{\isa{symmetric}}} & : & \isa{attribute} \\
1030 Calculational proof is forward reasoning with implicit application
1031 of transitivity rules (such those of \isa{{\isachardoublequote}{\isacharequal}{\isachardoublequote}}, \isa{{\isachardoublequote}{\isasymle}{\isachardoublequote}},
1032 \isa{{\isachardoublequote}{\isacharless}{\isachardoublequote}}). Isabelle/Isar maintains an auxiliary fact register
1033 \indexref{}{fact}{calculation}\hyperlink{fact.calculation}{\mbox{\isa{calculation}}} for accumulating results obtained by
1034 transitivity composed with the current result. Command \hyperlink{command.also}{\mbox{\isa{\isacommand{also}}}} updates \hyperlink{fact.calculation}{\mbox{\isa{calculation}}} involving \hyperlink{fact.this}{\mbox{\isa{this}}}, while
1035 \hyperlink{command.finally}{\mbox{\isa{\isacommand{finally}}}} exhibits the final \hyperlink{fact.calculation}{\mbox{\isa{calculation}}} by
1036 forward chaining towards the next goal statement. Both commands
1037 require valid current facts, i.e.\ may occur only after commands
1038 that produce theorems such as \hyperlink{command.assume}{\mbox{\isa{\isacommand{assume}}}}, \hyperlink{command.note}{\mbox{\isa{\isacommand{note}}}}, or some finished proof of \hyperlink{command.have}{\mbox{\isa{\isacommand{have}}}}, \hyperlink{command.show}{\mbox{\isa{\isacommand{show}}}} etc. The \hyperlink{command.moreover}{\mbox{\isa{\isacommand{moreover}}}} and \hyperlink{command.ultimately}{\mbox{\isa{\isacommand{ultimately}}}}
1039 commands are similar to \hyperlink{command.also}{\mbox{\isa{\isacommand{also}}}} and \hyperlink{command.finally}{\mbox{\isa{\isacommand{finally}}}},
1040 but only collect further results in \hyperlink{fact.calculation}{\mbox{\isa{calculation}}} without
1041 applying any rules yet.
1043 Also note that the implicit term abbreviation ``\isa{{\isachardoublequote}{\isasymdots}{\isachardoublequote}}'' has
1044 its canonical application with calculational proofs. It refers to
1045 the argument of the preceding statement. (The argument of a curried
1046 infix expression happens to be its right-hand side.)
1048 Isabelle/Isar calculations are implicitly subject to block structure
1049 in the sense that new threads of calculational reasoning are
1050 commenced for any new block (as opened by a local goal, for
1051 example). This means that, apart from being able to nest
1052 calculations, there is no separate \emph{begin-calculation} command
1055 \medskip The Isar calculation proof commands may be defined as
1056 follows:\footnote{We suppress internal bookkeeping such as proper
1057 handling of block-structure.}
1059 \begin{matharray}{rcl}
1060 \hyperlink{command.also}{\mbox{\isa{\isacommand{also}}}}\isa{{\isachardoublequote}\isactrlsub {\isadigit{0}}{\isachardoublequote}} & \equiv & \hyperlink{command.note}{\mbox{\isa{\isacommand{note}}}}~\isa{{\isachardoublequote}calculation\ {\isacharequal}\ this{\isachardoublequote}} \\
1061 \hyperlink{command.also}{\mbox{\isa{\isacommand{also}}}}\isa{{\isachardoublequote}\isactrlsub n\isactrlsub {\isacharplus}\isactrlsub {\isadigit{1}}{\isachardoublequote}} & \equiv & \hyperlink{command.note}{\mbox{\isa{\isacommand{note}}}}~\isa{{\isachardoublequote}calculation\ {\isacharequal}\ trans\ {\isacharbrackleft}OF\ calculation\ this{\isacharbrackright}{\isachardoublequote}} \\[0.5ex]
1062 \hyperlink{command.finally}{\mbox{\isa{\isacommand{finally}}}} & \equiv & \hyperlink{command.also}{\mbox{\isa{\isacommand{also}}}}~\hyperlink{command.from}{\mbox{\isa{\isacommand{from}}}}~\isa{calculation} \\[0.5ex]
1063 \hyperlink{command.moreover}{\mbox{\isa{\isacommand{moreover}}}} & \equiv & \hyperlink{command.note}{\mbox{\isa{\isacommand{note}}}}~\isa{{\isachardoublequote}calculation\ {\isacharequal}\ calculation\ this{\isachardoublequote}} \\
1064 \hyperlink{command.ultimately}{\mbox{\isa{\isacommand{ultimately}}}} & \equiv & \hyperlink{command.moreover}{\mbox{\isa{\isacommand{moreover}}}}~\hyperlink{command.from}{\mbox{\isa{\isacommand{from}}}}~\isa{calculation} \\
1068 ('also' | 'finally') ('(' thmrefs ')')?
1070 'trans' (() | 'add' | 'del')
1076 \item \hyperlink{command.also}{\mbox{\isa{\isacommand{also}}}}~\isa{{\isachardoublequote}{\isacharparenleft}a\isactrlsub {\isadigit{1}}\ {\isasymdots}\ a\isactrlsub n{\isacharparenright}{\isachardoublequote}} maintains the auxiliary
1077 \hyperlink{fact.calculation}{\mbox{\isa{calculation}}} register as follows. The first occurrence of
1078 \hyperlink{command.also}{\mbox{\isa{\isacommand{also}}}} in some calculational thread initializes \hyperlink{fact.calculation}{\mbox{\isa{calculation}}} by \hyperlink{fact.this}{\mbox{\isa{this}}}. Any subsequent \hyperlink{command.also}{\mbox{\isa{\isacommand{also}}}} on
1079 the same level of block-structure updates \hyperlink{fact.calculation}{\mbox{\isa{calculation}}} by
1080 some transitivity rule applied to \hyperlink{fact.calculation}{\mbox{\isa{calculation}}} and \hyperlink{fact.this}{\mbox{\isa{this}}} (in that order). Transitivity rules are picked from the
1081 current context, unless alternative rules are given as explicit
1084 \item \hyperlink{command.finally}{\mbox{\isa{\isacommand{finally}}}}~\isa{{\isachardoublequote}{\isacharparenleft}a\isactrlsub {\isadigit{1}}\ {\isasymdots}\ a\isactrlsub n{\isacharparenright}{\isachardoublequote}} maintaining \hyperlink{fact.calculation}{\mbox{\isa{calculation}}} in the same way as \hyperlink{command.also}{\mbox{\isa{\isacommand{also}}}}, and concludes the
1085 current calculational thread. The final result is exhibited as fact
1086 for forward chaining towards the next goal. Basically, \hyperlink{command.finally}{\mbox{\isa{\isacommand{finally}}}} just abbreviates \hyperlink{command.also}{\mbox{\isa{\isacommand{also}}}}~\hyperlink{command.from}{\mbox{\isa{\isacommand{from}}}}~\hyperlink{fact.calculation}{\mbox{\isa{calculation}}}. Typical idioms for concluding
1087 calculational proofs are ``\hyperlink{command.finally}{\mbox{\isa{\isacommand{finally}}}}~\hyperlink{command.show}{\mbox{\isa{\isacommand{show}}}}~\isa{{\isacharquery}thesis}~\hyperlink{command.dot}{\mbox{\isa{\isacommand{{\isachardot}}}}}'' and ``\hyperlink{command.finally}{\mbox{\isa{\isacommand{finally}}}}~\hyperlink{command.have}{\mbox{\isa{\isacommand{have}}}}~\isa{{\isasymphi}}~\hyperlink{command.dot}{\mbox{\isa{\isacommand{{\isachardot}}}}}''.
1089 \item \hyperlink{command.moreover}{\mbox{\isa{\isacommand{moreover}}}} and \hyperlink{command.ultimately}{\mbox{\isa{\isacommand{ultimately}}}} are
1090 analogous to \hyperlink{command.also}{\mbox{\isa{\isacommand{also}}}} and \hyperlink{command.finally}{\mbox{\isa{\isacommand{finally}}}}, but collect
1091 results only, without applying rules.
1093 \item \hyperlink{command.print-trans-rules}{\mbox{\isa{\isacommand{print{\isacharunderscore}trans{\isacharunderscore}rules}}}} prints the list of transitivity
1094 rules (for calculational commands \hyperlink{command.also}{\mbox{\isa{\isacommand{also}}}} and \hyperlink{command.finally}{\mbox{\isa{\isacommand{finally}}}}) and symmetry rules (for the \hyperlink{attribute.symmetric}{\mbox{\isa{symmetric}}}
1095 operation and single step elimination patters) of the current
1098 \item \hyperlink{attribute.trans}{\mbox{\isa{trans}}} declares theorems as transitivity rules.
1100 \item \hyperlink{attribute.sym}{\mbox{\isa{sym}}} declares symmetry rules, as well as
1101 \hyperlink{attribute.Pure.elim}{\mbox{\isa{Pure{\isachardot}elim}}}\isa{{\isachardoublequote}{\isacharquery}{\isachardoublequote}} rules.
1103 \item \hyperlink{attribute.symmetric}{\mbox{\isa{symmetric}}} resolves a theorem with some rule
1104 declared as \hyperlink{attribute.sym}{\mbox{\isa{sym}}} in the current context. For example,
1105 ``\hyperlink{command.assume}{\mbox{\isa{\isacommand{assume}}}}~\isa{{\isachardoublequote}{\isacharbrackleft}symmetric{\isacharbrackright}{\isacharcolon}\ x\ {\isacharequal}\ y{\isachardoublequote}}'' produces a
1106 swapped fact derived from that assumption.
1108 In structured proof texts it is often more appropriate to use an
1109 explicit single-step elimination proof, such as ``\hyperlink{command.assume}{\mbox{\isa{\isacommand{assume}}}}~\isa{{\isachardoublequote}x\ {\isacharequal}\ y{\isachardoublequote}}~\hyperlink{command.then}{\mbox{\isa{\isacommand{then}}}}~\hyperlink{command.have}{\mbox{\isa{\isacommand{have}}}}~\isa{{\isachardoublequote}y\ {\isacharequal}\ x{\isachardoublequote}}~\hyperlink{command.ddot}{\mbox{\isa{\isacommand{{\isachardot}{\isachardot}}}}}''.
1112 \end{isamarkuptext}%
1115 \isamarkupsection{Proof by cases and induction \label{sec:cases-induct}%
1119 \isamarkupsubsection{Rule contexts%
1123 \begin{isamarkuptext}%
1124 \begin{matharray}{rcl}
1125 \indexdef{}{command}{case}\hypertarget{command.case}{\hyperlink{command.case}{\mbox{\isa{\isacommand{case}}}}} & : & \isa{{\isachardoublequote}proof{\isacharparenleft}state{\isacharparenright}\ {\isasymrightarrow}\ proof{\isacharparenleft}state{\isacharparenright}{\isachardoublequote}} \\
1126 \indexdef{}{command}{print\_cases}\hypertarget{command.print-cases}{\hyperlink{command.print-cases}{\mbox{\isa{\isacommand{print{\isacharunderscore}cases}}}}}\isa{{\isachardoublequote}\isactrlsup {\isacharasterisk}{\isachardoublequote}} & : & \isa{{\isachardoublequote}context\ {\isasymrightarrow}{\isachardoublequote}} \\
1127 \indexdef{}{attribute}{case\_names}\hypertarget{attribute.case-names}{\hyperlink{attribute.case-names}{\mbox{\isa{case{\isacharunderscore}names}}}} & : & \isa{attribute} \\
1128 \indexdef{}{attribute}{case\_conclusion}\hypertarget{attribute.case-conclusion}{\hyperlink{attribute.case-conclusion}{\mbox{\isa{case{\isacharunderscore}conclusion}}}} & : & \isa{attribute} \\
1129 \indexdef{}{attribute}{params}\hypertarget{attribute.params}{\hyperlink{attribute.params}{\mbox{\isa{params}}}} & : & \isa{attribute} \\
1130 \indexdef{}{attribute}{consumes}\hypertarget{attribute.consumes}{\hyperlink{attribute.consumes}{\mbox{\isa{consumes}}}} & : & \isa{attribute} \\
1133 The puristic way to build up Isar proof contexts is by explicit
1134 language elements like \hyperlink{command.fix}{\mbox{\isa{\isacommand{fix}}}}, \hyperlink{command.assume}{\mbox{\isa{\isacommand{assume}}}},
1135 \hyperlink{command.let}{\mbox{\isa{\isacommand{let}}}} (see \secref{sec:proof-context}). This is adequate
1136 for plain natural deduction, but easily becomes unwieldy in concrete
1137 verification tasks, which typically involve big induction rules with
1140 The \hyperlink{command.case}{\mbox{\isa{\isacommand{case}}}} command provides a shorthand to refer to a
1141 local context symbolically: certain proof methods provide an
1142 environment of named ``cases'' of the form \isa{{\isachardoublequote}c{\isacharcolon}\ x\isactrlsub {\isadigit{1}}{\isacharcomma}\ {\isasymdots}{\isacharcomma}\ x\isactrlsub m{\isacharcomma}\ {\isasymphi}\isactrlsub {\isadigit{1}}{\isacharcomma}\ {\isasymdots}{\isacharcomma}\ {\isasymphi}\isactrlsub n{\isachardoublequote}}; the effect of ``\hyperlink{command.case}{\mbox{\isa{\isacommand{case}}}}~\isa{c}'' is then equivalent to ``\hyperlink{command.fix}{\mbox{\isa{\isacommand{fix}}}}~\isa{{\isachardoublequote}x\isactrlsub {\isadigit{1}}\ {\isasymdots}\ x\isactrlsub m{\isachardoublequote}}~\hyperlink{command.assume}{\mbox{\isa{\isacommand{assume}}}}~\isa{{\isachardoublequote}c{\isacharcolon}\ {\isasymphi}\isactrlsub {\isadigit{1}}\ {\isasymdots}\ {\isasymphi}\isactrlsub n{\isachardoublequote}}''. Term bindings may be covered as well, notably
1143 \hyperlink{variable.?case}{\mbox{\isa{{\isacharquery}case}}} for the main conclusion.
1145 By default, the ``terminology'' \isa{{\isachardoublequote}x\isactrlsub {\isadigit{1}}{\isacharcomma}\ {\isasymdots}{\isacharcomma}\ x\isactrlsub m{\isachardoublequote}} of
1146 a case value is marked as hidden, i.e.\ there is no way to refer to
1147 such parameters in the subsequent proof text. After all, original
1148 rule parameters stem from somewhere outside of the current proof
1149 text. By using the explicit form ``\hyperlink{command.case}{\mbox{\isa{\isacommand{case}}}}~\isa{{\isachardoublequote}{\isacharparenleft}c\ y\isactrlsub {\isadigit{1}}\ {\isasymdots}\ y\isactrlsub m{\isacharparenright}{\isachardoublequote}}'' instead, the proof author is able to
1150 chose local names that fit nicely into the current context.
1152 \medskip It is important to note that proper use of \hyperlink{command.case}{\mbox{\isa{\isacommand{case}}}} does not provide means to peek at the current goal state,
1153 which is not directly observable in Isar! Nonetheless, goal
1154 refinement commands do provide named cases \isa{{\isachardoublequote}goal\isactrlsub i{\isachardoublequote}}
1155 for each subgoal \isa{{\isachardoublequote}i\ {\isacharequal}\ {\isadigit{1}}{\isacharcomma}\ {\isasymdots}{\isacharcomma}\ n{\isachardoublequote}} of the resulting goal state.
1156 Using this extra feature requires great care, because some bits of
1157 the internal tactical machinery intrude the proof text. In
1158 particular, parameter names stemming from the left-over of automated
1159 reasoning tools are usually quite unpredictable.
1161 Under normal circumstances, the text of cases emerge from standard
1162 elimination or induction rules, which in turn are derived from
1163 previous theory specifications in a canonical way (say from
1164 \hyperlink{command.inductive}{\mbox{\isa{\isacommand{inductive}}}} definitions).
1166 \medskip Proper cases are only available if both the proof method
1167 and the rules involved support this. By using appropriate
1168 attributes, case names, conclusions, and parameters may be also
1169 declared by hand. Thus variant versions of rules that have been
1170 derived manually become ready to use in advanced case analysis
1174 'case' (caseref | '(' caseref ((name | underscore) +) ')')
1176 caseref: nameref attributes?
1179 'case\_names' (name +)
1181 'case\_conclusion' name (name *)
1183 'params' ((name *) + 'and')
1191 \item \hyperlink{command.case}{\mbox{\isa{\isacommand{case}}}}~\isa{{\isachardoublequote}{\isacharparenleft}c\ x\isactrlsub {\isadigit{1}}\ {\isasymdots}\ x\isactrlsub m{\isacharparenright}{\isachardoublequote}} invokes a named local
1192 context \isa{{\isachardoublequote}c{\isacharcolon}\ x\isactrlsub {\isadigit{1}}{\isacharcomma}\ {\isasymdots}{\isacharcomma}\ x\isactrlsub m{\isacharcomma}\ {\isasymphi}\isactrlsub {\isadigit{1}}{\isacharcomma}\ {\isasymdots}{\isacharcomma}\ {\isasymphi}\isactrlsub m{\isachardoublequote}}, as provided by an
1193 appropriate proof method (such as \indexref{}{method}{cases}\hyperlink{method.cases}{\mbox{\isa{cases}}} and
1194 \indexref{}{method}{induct}\hyperlink{method.induct}{\mbox{\isa{induct}}}). The command ``\hyperlink{command.case}{\mbox{\isa{\isacommand{case}}}}~\isa{{\isachardoublequote}{\isacharparenleft}c\ x\isactrlsub {\isadigit{1}}\ {\isasymdots}\ x\isactrlsub m{\isacharparenright}{\isachardoublequote}}'' abbreviates ``\hyperlink{command.fix}{\mbox{\isa{\isacommand{fix}}}}~\isa{{\isachardoublequote}x\isactrlsub {\isadigit{1}}\ {\isasymdots}\ x\isactrlsub m{\isachardoublequote}}~\hyperlink{command.assume}{\mbox{\isa{\isacommand{assume}}}}~\isa{{\isachardoublequote}c{\isacharcolon}\ {\isasymphi}\isactrlsub {\isadigit{1}}\ {\isasymdots}\ {\isasymphi}\isactrlsub n{\isachardoublequote}}''.
1196 \item \hyperlink{command.print-cases}{\mbox{\isa{\isacommand{print{\isacharunderscore}cases}}}} prints all local contexts of the
1197 current state, using Isar proof language notation.
1199 \item \hyperlink{attribute.case-names}{\mbox{\isa{case{\isacharunderscore}names}}}~\isa{{\isachardoublequote}c\isactrlsub {\isadigit{1}}\ {\isasymdots}\ c\isactrlsub k{\isachardoublequote}} declares names for
1200 the local contexts of premises of a theorem; \isa{{\isachardoublequote}c\isactrlsub {\isadigit{1}}{\isacharcomma}\ {\isasymdots}{\isacharcomma}\ c\isactrlsub k{\isachardoublequote}}
1201 refers to the \emph{suffix} of the list of premises.
1203 \item \hyperlink{attribute.case-conclusion}{\mbox{\isa{case{\isacharunderscore}conclusion}}}~\isa{{\isachardoublequote}c\ d\isactrlsub {\isadigit{1}}\ {\isasymdots}\ d\isactrlsub k{\isachardoublequote}} declares
1204 names for the conclusions of a named premise \isa{c}; here \isa{{\isachardoublequote}d\isactrlsub {\isadigit{1}}{\isacharcomma}\ {\isasymdots}{\isacharcomma}\ d\isactrlsub k{\isachardoublequote}} refers to the prefix of arguments of a logical formula
1205 built by nesting a binary connective (e.g.\ \isa{{\isachardoublequote}{\isasymor}{\isachardoublequote}}).
1207 Note that proof methods such as \hyperlink{method.induct}{\mbox{\isa{induct}}} and \hyperlink{method.coinduct}{\mbox{\isa{coinduct}}} already provide a default name for the conclusion as a
1208 whole. The need to name subformulas only arises with cases that
1209 split into several sub-cases, as in common co-induction rules.
1211 \item \hyperlink{attribute.params}{\mbox{\isa{params}}}~\isa{{\isachardoublequote}p\isactrlsub {\isadigit{1}}\ {\isasymdots}\ p\isactrlsub m\ {\isasymAND}\ {\isasymdots}\ q\isactrlsub {\isadigit{1}}\ {\isasymdots}\ q\isactrlsub n{\isachardoublequote}} renames
1212 the innermost parameters of premises \isa{{\isachardoublequote}{\isadigit{1}}{\isacharcomma}\ {\isasymdots}{\isacharcomma}\ n{\isachardoublequote}} of some
1213 theorem. An empty list of names may be given to skip positions,
1214 leaving the present parameters unchanged.
1216 Note that the default usage of case rules does \emph{not} directly
1217 expose parameters to the proof context.
1219 \item \hyperlink{attribute.consumes}{\mbox{\isa{consumes}}}~\isa{n} declares the number of ``major
1220 premises'' of a rule, i.e.\ the number of facts to be consumed when
1221 it is applied by an appropriate proof method. The default value of
1222 \hyperlink{attribute.consumes}{\mbox{\isa{consumes}}} is \isa{{\isachardoublequote}n\ {\isacharequal}\ {\isadigit{1}}{\isachardoublequote}}, which is appropriate for
1223 the usual kind of cases and induction rules for inductive sets (cf.\
1224 \secref{sec:hol-inductive}). Rules without any \hyperlink{attribute.consumes}{\mbox{\isa{consumes}}} declaration given are treated as if \hyperlink{attribute.consumes}{\mbox{\isa{consumes}}}~\isa{{\isadigit{0}}} had been specified.
1226 Note that explicit \hyperlink{attribute.consumes}{\mbox{\isa{consumes}}} declarations are only
1227 rarely needed; this is already taken care of automatically by the
1228 higher-level \hyperlink{attribute.cases}{\mbox{\isa{cases}}}, \hyperlink{attribute.induct}{\mbox{\isa{induct}}}, and
1229 \hyperlink{attribute.coinduct}{\mbox{\isa{coinduct}}} declarations.
1232 \end{isamarkuptext}%
1235 \isamarkupsubsection{Proof methods%
1239 \begin{isamarkuptext}%
1240 \begin{matharray}{rcl}
1241 \indexdef{}{method}{cases}\hypertarget{method.cases}{\hyperlink{method.cases}{\mbox{\isa{cases}}}} & : & \isa{method} \\
1242 \indexdef{}{method}{induct}\hypertarget{method.induct}{\hyperlink{method.induct}{\mbox{\isa{induct}}}} & : & \isa{method} \\
1243 \indexdef{}{method}{coinduct}\hypertarget{method.coinduct}{\hyperlink{method.coinduct}{\mbox{\isa{coinduct}}}} & : & \isa{method} \\
1246 The \hyperlink{method.cases}{\mbox{\isa{cases}}}, \hyperlink{method.induct}{\mbox{\isa{induct}}}, and \hyperlink{method.coinduct}{\mbox{\isa{coinduct}}}
1247 methods provide a uniform interface to common proof techniques over
1248 datatypes, inductive predicates (or sets), recursive functions etc.
1249 The corresponding rules may be specified and instantiated in a
1250 casual manner. Furthermore, these methods provide named local
1251 contexts that may be invoked via the \hyperlink{command.case}{\mbox{\isa{\isacommand{case}}}} proof command
1252 within the subsequent proof text. This accommodates compact proof
1253 texts even when reasoning about large specifications.
1255 The \hyperlink{method.induct}{\mbox{\isa{induct}}} method also provides some additional
1256 infrastructure in order to be applicable to structure statements
1257 (either using explicit meta-level connectives, or including facts
1258 and parameters separately). This avoids cumbersome encoding of
1259 ``strengthened'' inductive statements within the object-logic.
1262 'cases' (insts * 'and') rule?
1264 'induct' (definsts * 'and') \\ arbitrary? taking? rule?
1266 'coinduct' insts taking rule?
1269 rule: ('type' | 'pred' | 'set') ':' (nameref +) | 'rule' ':' (thmref +)
1271 definst: name ('==' | equiv) term | inst
1273 definsts: ( definst *)
1275 arbitrary: 'arbitrary' ':' ((term *) 'and' +)
1277 taking: 'taking' ':' insts
1283 \item \hyperlink{method.cases}{\mbox{\isa{cases}}}~\isa{{\isachardoublequote}insts\ R{\isachardoublequote}} applies method \hyperlink{method.rule}{\mbox{\isa{rule}}} with an appropriate case distinction theorem, instantiated to
1284 the subjects \isa{insts}. Symbolic case names are bound according
1285 to the rule's local contexts.
1287 The rule is determined as follows, according to the facts and
1288 arguments passed to the \hyperlink{method.cases}{\mbox{\isa{cases}}} method:
1291 \begin{tabular}{llll}
1292 facts & & arguments & rule \\\hline
1293 & \hyperlink{method.cases}{\mbox{\isa{cases}}} & & classical case split \\
1294 & \hyperlink{method.cases}{\mbox{\isa{cases}}} & \isa{t} & datatype exhaustion (type of \isa{t}) \\
1295 \isa{{\isachardoublequote}{\isasymturnstile}\ A\ t{\isachardoublequote}} & \hyperlink{method.cases}{\mbox{\isa{cases}}} & \isa{{\isachardoublequote}{\isasymdots}{\isachardoublequote}} & inductive predicate/set elimination (of \isa{A}) \\
1296 \isa{{\isachardoublequote}{\isasymdots}{\isachardoublequote}} & \hyperlink{method.cases}{\mbox{\isa{cases}}} & \isa{{\isachardoublequote}{\isasymdots}\ rule{\isacharcolon}\ R{\isachardoublequote}} & explicit rule \isa{R} \\
1300 Several instantiations may be given, referring to the \emph{suffix}
1301 of premises of the case rule; within each premise, the \emph{prefix}
1302 of variables is instantiated. In most situations, only a single
1303 term needs to be specified; this refers to the first variable of the
1304 last premise (it is usually the same for all cases).
1306 \item \hyperlink{method.induct}{\mbox{\isa{induct}}}~\isa{{\isachardoublequote}insts\ R{\isachardoublequote}} is analogous to the
1307 \hyperlink{method.cases}{\mbox{\isa{cases}}} method, but refers to induction rules, which are
1308 determined as follows:
1311 \begin{tabular}{llll}
1312 facts & & arguments & rule \\\hline
1313 & \hyperlink{method.induct}{\mbox{\isa{induct}}} & \isa{{\isachardoublequote}P\ x{\isachardoublequote}} & datatype induction (type of \isa{x}) \\
1314 \isa{{\isachardoublequote}{\isasymturnstile}\ A\ x{\isachardoublequote}} & \hyperlink{method.induct}{\mbox{\isa{induct}}} & \isa{{\isachardoublequote}{\isasymdots}{\isachardoublequote}} & predicate/set induction (of \isa{A}) \\
1315 \isa{{\isachardoublequote}{\isasymdots}{\isachardoublequote}} & \hyperlink{method.induct}{\mbox{\isa{induct}}} & \isa{{\isachardoublequote}{\isasymdots}\ rule{\isacharcolon}\ R{\isachardoublequote}} & explicit rule \isa{R} \\
1319 Several instantiations may be given, each referring to some part of
1320 a mutual inductive definition or datatype --- only related partial
1321 induction rules may be used together, though. Any of the lists of
1322 terms \isa{{\isachardoublequote}P{\isacharcomma}\ x{\isacharcomma}\ {\isasymdots}{\isachardoublequote}} refers to the \emph{suffix} of variables
1323 present in the induction rule. This enables the writer to specify
1324 only induction variables, or both predicates and variables, for
1327 Instantiations may be definitional: equations \isa{{\isachardoublequote}x\ {\isasymequiv}\ t{\isachardoublequote}}
1328 introduce local definitions, which are inserted into the claim and
1329 discharged after applying the induction rule. Equalities reappear
1330 in the inductive cases, but have been transformed according to the
1331 induction principle being involved here. In order to achieve
1332 practically useful induction hypotheses, some variables occurring in
1333 \isa{t} need to be fixed (see below).
1335 The optional ``\isa{{\isachardoublequote}arbitrary{\isacharcolon}\ x\isactrlsub {\isadigit{1}}\ {\isasymdots}\ x\isactrlsub m{\isachardoublequote}}''
1336 specification generalizes variables \isa{{\isachardoublequote}x\isactrlsub {\isadigit{1}}{\isacharcomma}\ {\isasymdots}{\isacharcomma}\ x\isactrlsub m{\isachardoublequote}} of the original goal before applying induction. Thus
1337 induction hypotheses may become sufficiently general to get the
1338 proof through. Together with definitional instantiations, one may
1339 effectively perform induction over expressions of a certain
1342 The optional ``\isa{{\isachardoublequote}taking{\isacharcolon}\ t\isactrlsub {\isadigit{1}}\ {\isasymdots}\ t\isactrlsub n{\isachardoublequote}}''
1343 specification provides additional instantiations of a prefix of
1344 pending variables in the rule. Such schematic induction rules
1345 rarely occur in practice, though.
1347 \item \hyperlink{method.coinduct}{\mbox{\isa{coinduct}}}~\isa{{\isachardoublequote}inst\ R{\isachardoublequote}} is analogous to the
1348 \hyperlink{method.induct}{\mbox{\isa{induct}}} method, but refers to coinduction rules, which are
1349 determined as follows:
1352 \begin{tabular}{llll}
1353 goal & & arguments & rule \\\hline
1354 & \hyperlink{method.coinduct}{\mbox{\isa{coinduct}}} & \isa{x} & type coinduction (type of \isa{x}) \\
1355 \isa{{\isachardoublequote}A\ x{\isachardoublequote}} & \hyperlink{method.coinduct}{\mbox{\isa{coinduct}}} & \isa{{\isachardoublequote}{\isasymdots}{\isachardoublequote}} & predicate/set coinduction (of \isa{A}) \\
1356 \isa{{\isachardoublequote}{\isasymdots}{\isachardoublequote}} & \hyperlink{method.coinduct}{\mbox{\isa{coinduct}}} & \isa{{\isachardoublequote}{\isasymdots}\ rule{\isacharcolon}\ R{\isachardoublequote}} & explicit rule \isa{R} \\
1359 Coinduction is the dual of induction. Induction essentially
1360 eliminates \isa{{\isachardoublequote}A\ x{\isachardoublequote}} towards a generic result \isa{{\isachardoublequote}P\ x{\isachardoublequote}},
1361 while coinduction introduces \isa{{\isachardoublequote}A\ x{\isachardoublequote}} starting with \isa{{\isachardoublequote}B\ x{\isachardoublequote}}, for a suitable ``bisimulation'' \isa{B}. The cases of a
1362 coinduct rule are typically named after the predicates or sets being
1363 covered, while the conclusions consist of several alternatives being
1364 named after the individual destructor patterns.
1366 The given instantiation refers to the \emph{suffix} of variables
1367 occurring in the rule's major premise, or conclusion if unavailable.
1368 An additional ``\isa{{\isachardoublequote}taking{\isacharcolon}\ t\isactrlsub {\isadigit{1}}\ {\isasymdots}\ t\isactrlsub n{\isachardoublequote}}''
1369 specification may be required in order to specify the bisimulation
1370 to be used in the coinduction step.
1374 Above methods produce named local contexts, as determined by the
1375 instantiated rule as given in the text. Beyond that, the \hyperlink{method.induct}{\mbox{\isa{induct}}} and \hyperlink{method.coinduct}{\mbox{\isa{coinduct}}} methods guess further instantiations
1376 from the goal specification itself. Any persisting unresolved
1377 schematic variables of the resulting rule will render the the
1378 corresponding case invalid. The term binding \hyperlink{variable.?case}{\mbox{\isa{{\isacharquery}case}}} for
1379 the conclusion will be provided with each case, provided that term
1382 The \hyperlink{command.print-cases}{\mbox{\isa{\isacommand{print{\isacharunderscore}cases}}}} command prints all named cases present
1383 in the current proof state.
1385 \medskip Despite the additional infrastructure, both \hyperlink{method.cases}{\mbox{\isa{cases}}}
1386 and \hyperlink{method.coinduct}{\mbox{\isa{coinduct}}} merely apply a certain rule, after
1387 instantiation, while conforming due to the usual way of monotonic
1388 natural deduction: the context of a structured statement \isa{{\isachardoublequote}{\isasymAnd}x\isactrlsub {\isadigit{1}}\ {\isasymdots}\ x\isactrlsub m{\isachardot}\ {\isasymphi}\isactrlsub {\isadigit{1}}\ {\isasymLongrightarrow}\ {\isasymdots}\ {\isasymphi}\isactrlsub n\ {\isasymLongrightarrow}\ {\isasymdots}{\isachardoublequote}}
1389 reappears unchanged after the case split.
1391 The \hyperlink{method.induct}{\mbox{\isa{induct}}} method is fundamentally different in this
1392 respect: the meta-level structure is passed through the
1393 ``recursive'' course involved in the induction. Thus the original
1394 statement is basically replaced by separate copies, corresponding to
1395 the induction hypotheses and conclusion; the original goal context
1396 is no longer available. Thus local assumptions, fixed parameters
1397 and definitions effectively participate in the inductive rephrasing
1398 of the original statement.
1400 In induction proofs, local assumptions introduced by cases are split
1401 into two different kinds: \isa{hyps} stemming from the rule and
1402 \isa{prems} from the goal statement. This is reflected in the
1403 extracted cases accordingly, so invoking ``\hyperlink{command.case}{\mbox{\isa{\isacommand{case}}}}~\isa{c}'' will provide separate facts \isa{c{\isachardot}hyps} and \isa{c{\isachardot}prems},
1404 as well as fact \isa{c} to hold the all-inclusive list.
1406 \medskip Facts presented to either method are consumed according to
1407 the number of ``major premises'' of the rule involved, which is
1408 usually 0 for plain cases and induction rules of datatypes etc.\ and
1409 1 for rules of inductive predicates or sets and the like. The
1410 remaining facts are inserted into the goal verbatim before the
1411 actual \isa{cases}, \isa{induct}, or \isa{coinduct} rule is
1413 \end{isamarkuptext}%
1416 \isamarkupsubsection{Declaring rules%
1420 \begin{isamarkuptext}%
1421 \begin{matharray}{rcl}
1422 \indexdef{}{command}{print\_induct\_rules}\hypertarget{command.print-induct-rules}{\hyperlink{command.print-induct-rules}{\mbox{\isa{\isacommand{print{\isacharunderscore}induct{\isacharunderscore}rules}}}}}\isa{{\isachardoublequote}\isactrlsup {\isacharasterisk}{\isachardoublequote}} & : & \isa{{\isachardoublequote}context\ {\isasymrightarrow}{\isachardoublequote}} \\
1423 \indexdef{}{attribute}{cases}\hypertarget{attribute.cases}{\hyperlink{attribute.cases}{\mbox{\isa{cases}}}} & : & \isa{attribute} \\
1424 \indexdef{}{attribute}{induct}\hypertarget{attribute.induct}{\hyperlink{attribute.induct}{\mbox{\isa{induct}}}} & : & \isa{attribute} \\
1425 \indexdef{}{attribute}{coinduct}\hypertarget{attribute.coinduct}{\hyperlink{attribute.coinduct}{\mbox{\isa{coinduct}}}} & : & \isa{attribute} \\
1436 spec: (('type' | 'pred' | 'set') ':' nameref) | 'del'
1442 \item \hyperlink{command.print-induct-rules}{\mbox{\isa{\isacommand{print{\isacharunderscore}induct{\isacharunderscore}rules}}}} prints cases and induct rules
1443 for predicates (or sets) and types of the current context.
1445 \item \hyperlink{attribute.cases}{\mbox{\isa{cases}}}, \hyperlink{attribute.induct}{\mbox{\isa{induct}}}, and \hyperlink{attribute.coinduct}{\mbox{\isa{coinduct}}} (as attributes) declare rules for reasoning about
1446 (co)inductive predicates (or sets) and types, using the
1447 corresponding methods of the same name. Certain definitional
1448 packages of object-logics usually declare emerging cases and
1449 induction rules as expected, so users rarely need to intervene.
1451 Rules may be deleted via the \isa{{\isachardoublequote}del{\isachardoublequote}} specification, which
1452 covers all of the \isa{{\isachardoublequote}type{\isachardoublequote}}/\isa{{\isachardoublequote}pred{\isachardoublequote}}/\isa{{\isachardoublequote}set{\isachardoublequote}}
1453 sub-categories simultaneously. For example, \hyperlink{attribute.cases}{\mbox{\isa{cases}}}~\isa{del} removes any \hyperlink{attribute.cases}{\mbox{\isa{cases}}} rules declared for
1454 some type, predicate, or set.
1456 Manual rule declarations usually refer to the \hyperlink{attribute.case-names}{\mbox{\isa{case{\isacharunderscore}names}}} and \hyperlink{attribute.params}{\mbox{\isa{params}}} attributes to adjust names of
1457 cases and parameters of a rule; the \hyperlink{attribute.consumes}{\mbox{\isa{consumes}}}
1458 declaration is taken care of automatically: \hyperlink{attribute.consumes}{\mbox{\isa{consumes}}}~\isa{{\isadigit{0}}} is specified for ``type'' rules and \hyperlink{attribute.consumes}{\mbox{\isa{consumes}}}~\isa{{\isadigit{1}}} for ``predicate'' / ``set'' rules.
1461 \end{isamarkuptext}%
1469 \isacommand{end}\isamarkupfalse%
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