wenzelm@30184
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\chapter{Theorems and Forward Proof}
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\index{theorems|(}
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Theorems, which represent the axioms, theorems and rules of
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object-logics, have type \mltydx{thm}. This chapter begins by
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describing operations that print theorems and that join them in
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forward proof. Most theorem operations are intended for advanced
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applications, such as programming new proof procedures. Many of these
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operations refer to signatures, certified terms and certified types,
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which have the \ML{} types {\tt Sign.sg}, {\tt cterm} and {\tt ctyp}
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and are discussed in Chapter~\ref{theories}. Beginning users should
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ignore such complexities --- and skip all but the first section of
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this chapter.
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\section{Basic operations on theorems}
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\subsection{Pretty-printing a theorem}
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\index{theorems!printing of}
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\begin{ttbox}
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prth : thm -> thm
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prths : thm list -> thm list
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prthq : thm Seq.seq -> thm Seq.seq
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print_thm : thm -> unit
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print_goals : int -> thm -> unit
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string_of_thm : thm -> string
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\end{ttbox}
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The first three commands are for interactive use. They are identity
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functions that display, then return, their argument. The \ML{} identifier
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{\tt it} will refer to the value just displayed.
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The others are for use in programs. Functions with result type {\tt unit}
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are convenient for imperative programming.
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\begin{ttdescription}
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\item[\ttindexbold{prth} {\it thm}]
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prints {\it thm\/} at the terminal.
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\item[\ttindexbold{prths} {\it thms}]
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prints {\it thms}, a list of theorems.
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\item[\ttindexbold{prthq} {\it thmq}]
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prints {\it thmq}, a sequence of theorems. It is useful for inspecting
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the output of a tactic.
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\item[\ttindexbold{print_thm} {\it thm}]
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prints {\it thm\/} at the terminal.
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\item[\ttindexbold{print_goals} {\it limit\/} {\it thm}]
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prints {\it thm\/} in goal style, with the premises as subgoals. It prints
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at most {\it limit\/} subgoals. The subgoal module calls {\tt print_goals}
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to display proof states.
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\item[\ttindexbold{string_of_thm} {\it thm}]
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converts {\it thm\/} to a string.
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\end{ttdescription}
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\subsection{Forward proof: joining rules by resolution}
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\index{theorems!joining by resolution}
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\index{resolution}\index{forward proof}
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\begin{ttbox}
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RSN : thm * (int * thm) -> thm \hfill\textbf{infix}
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RS : thm * thm -> thm \hfill\textbf{infix}
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MRS : thm list * thm -> thm \hfill\textbf{infix}
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OF : thm * thm list -> thm \hfill\textbf{infix}
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RLN : thm list * (int * thm list) -> thm list \hfill\textbf{infix}
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RL : thm list * thm list -> thm list \hfill\textbf{infix}
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MRL : thm list list * thm list -> thm list \hfill\textbf{infix}
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\end{ttbox}
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Joining rules together is a simple way of deriving new rules. These
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functions are especially useful with destruction rules. To store
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the result in the theorem database, use \ttindex{bind_thm}
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(\S\ref{ExtractingAndStoringTheProvedTheorem}).
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\begin{ttdescription}
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\item[\tt$thm@1$ RSN $(i,thm@2)$] \indexbold{*RSN}
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resolves the conclusion of $thm@1$ with the $i$th premise of~$thm@2$.
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Unless there is precisely one resolvent it raises exception
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\xdx{THM}; in that case, use {\tt RLN}.
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\item[\tt$thm@1$ RS $thm@2$] \indexbold{*RS}
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abbreviates \hbox{\tt$thm@1$ RSN $(1,thm@2)$}. Thus, it resolves the
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conclusion of $thm@1$ with the first premise of~$thm@2$.
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\item[\tt {$[thm@1,\ldots,thm@n]$} MRS $thm$] \indexbold{*MRS}
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uses {\tt RSN} to resolve $thm@i$ against premise~$i$ of $thm$, for
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$i=n$, \ldots,~1. This applies $thm@n$, \ldots, $thm@1$ to the first $n$
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premises of $thm$. Because the theorems are used from right to left, it
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does not matter if the $thm@i$ create new premises. {\tt MRS} is useful
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for expressing proof trees.
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\item[\tt {$thm$ OF $[thm@1,\ldots,thm@n]$}] \indexbold{*OF} is the same as
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\texttt{$[thm@1,\ldots,thm@n]$ MRS $thm$}, with slightly more readable
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argument order, though.
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\item[\tt$thms@1$ RLN $(i,thms@2)$] \indexbold{*RLN}
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joins lists of theorems. For every $thm@1$ in $thms@1$ and $thm@2$ in
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$thms@2$, it resolves the conclusion of $thm@1$ with the $i$th premise
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of~$thm@2$, accumulating the results.
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\item[\tt$thms@1$ RL $thms@2$] \indexbold{*RL}
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abbreviates \hbox{\tt$thms@1$ RLN $(1,thms@2)$}.
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\item[\tt {$[thms@1,\ldots,thms@n]$} MRL $thms$] \indexbold{*MRL}
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is analogous to {\tt MRS}, but combines theorem lists rather than theorems.
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It too is useful for expressing proof trees.
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\end{ttdescription}
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\subsection{Expanding definitions in theorems}
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\index{meta-rewriting!in theorems}
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\begin{ttbox}
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rewrite_rule : thm list -> thm -> thm
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rewrite_goals_rule : thm list -> thm -> thm
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\end{ttbox}
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\begin{ttdescription}
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\item[\ttindexbold{rewrite_rule} {\it defs} {\it thm}]
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unfolds the {\it defs} throughout the theorem~{\it thm}.
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\item[\ttindexbold{rewrite_goals_rule} {\it defs} {\it thm}]
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unfolds the {\it defs} in the premises of~{\it thm}, but it leaves the
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conclusion unchanged. This rule is the basis for \ttindex{rewrite_goals_tac},
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but it serves little purpose in forward proof.
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\end{ttdescription}
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\subsection{Instantiating unknowns in a theorem} \label{sec:instantiate}
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\index{instantiation}
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\begin{alltt}\footnotesize
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read_instantiate : (string*string) list -> thm -> thm
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read_instantiate_sg : Sign.sg -> (string*string) list -> thm -> thm
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cterm_instantiate : (cterm*cterm) list -> thm -> thm
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instantiate' : ctyp option list -> cterm option list -> thm -> thm
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\end{alltt}
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These meta-rules instantiate type and term unknowns in a theorem. They are
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occasionally useful. They can prevent difficulties with higher-order
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unification, and define specialized versions of rules.
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\begin{ttdescription}
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\item[\ttindexbold{read_instantiate} {\it insts} {\it thm}]
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processes the instantiations {\it insts} and instantiates the rule~{\it
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thm}. The processing of instantiations is described
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in \S\ref{res_inst_tac}, under {\tt res_inst_tac}.
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Use {\tt res_inst_tac}, not {\tt read_instantiate}, to instantiate a rule
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and refine a particular subgoal. The tactic allows instantiation by the
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subgoal's parameters, and reads the instantiations using the signature
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associated with the proof state.
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Use {\tt read_instantiate_sg} below if {\it insts\/} appears to be treated
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incorrectly.
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\item[\ttindexbold{read_instantiate_sg} {\it sg} {\it insts} {\it thm}]
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is like \texttt{read_instantiate {\it insts}~{\it thm}}, but it reads
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the instantiations under signature~{\it sg}. This is necessary to
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instantiate a rule from a general theory, such as first-order logic,
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using the notation of some specialized theory. Use the function {\tt
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sign_of} to get a theory's signature.
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\item[\ttindexbold{cterm_instantiate} {\it ctpairs} {\it thm}]
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is similar to {\tt read_instantiate}, but the instantiations are provided
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as pairs of certified terms, not as strings to be read.
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\item[\ttindexbold{instantiate'} {\it ctyps} {\it cterms} {\it thm}]
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instantiates {\it thm} according to the positional arguments {\it
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ctyps} and {\it cterms}. Counting from left to right, schematic
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variables $?x$ are either replaced by $t$ for any argument
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\texttt{Some\(\;t\)}, or left unchanged in case of \texttt{None} or
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if the end of the argument list is encountered. Types are
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instantiated before terms.
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\end{ttdescription}
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\subsection{Miscellaneous forward rules}\label{MiscellaneousForwardRules}
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\index{theorems!standardizing}
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\begin{ttbox}
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standard : thm -> thm
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zero_var_indexes : thm -> thm
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make_elim : thm -> thm
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rule_by_tactic : tactic -> thm -> thm
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rotate_prems : int -> thm -> thm
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permute_prems : int -> int -> thm -> thm
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rearrange_prems : int list -> thm -> thm
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\end{ttbox}
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\begin{ttdescription}
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\item[\ttindexbold{standard} $thm$] puts $thm$ into the standard form
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of object-rules. It discharges all meta-assumptions, replaces free
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variables by schematic variables, renames schematic variables to
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have subscript zero, also strips outer (meta) quantifiers and
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removes dangling sort hypotheses.
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\item[\ttindexbold{zero_var_indexes} $thm$]
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makes all schematic variables have subscript zero, renaming them to avoid
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clashes.
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\item[\ttindexbold{make_elim} $thm$]
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\index{rules!converting destruction to elimination}
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converts $thm$, which should be a destruction rule of the form
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$\List{P@1;\ldots;P@m}\Imp
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Q$, to the elimination rule $\List{P@1; \ldots; P@m; Q\Imp R}\Imp R$. This
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is the basis for destruct-resolution: {\tt dresolve_tac}, etc.
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\item[\ttindexbold{rule_by_tactic} {\it tac} {\it thm}]
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applies {\it tac\/} to the {\it thm}, freezing its variables first, then
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yields the proof state returned by the tactic. In typical usage, the
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{\it thm\/} represents an instance of a rule with several premises, some
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with contradictory assumptions (because of the instantiation). The
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tactic proves those subgoals and does whatever else it can, and returns
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whatever is left.
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\item[\ttindexbold{rotate_prems} $k$ $thm$] rotates the premises of $thm$ to
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the left by~$k$ positions (to the right if $k<0$). It simply calls
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\texttt{permute_prems}, below, with $j=0$. Used with
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\texttt{eresolve_tac}\index{*eresolve_tac!on other than first premise}, it
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gives the effect of applying the tactic to some other premise of $thm$ than
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the first.
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\item[\ttindexbold{permute_prems} $j$ $k$ $thm$] rotates the premises of $thm$
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leaving the first $j$ premises unchanged. It
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requires $0\leq j\leq n$, where $n$ is the number of premises. If $k$ is
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positive then it rotates the remaining $n-j$ premises to the left; if $k$ is
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negative then it rotates the premises to the right.
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\item[\ttindexbold{rearrange_prems} $ps$ $thm$] permutes the premises of $thm$
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where the value at the $i$-th position (counting from $0$) in the list $ps$
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gives the position within the original thm to be transferred to position $i$.
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Any remaining trailing positions are left unchanged.
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\end{ttdescription}
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\subsection{Taking a theorem apart}
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\index{theorems!taking apart}
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\index{flex-flex constraints}
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\begin{ttbox}
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cprop_of : thm -> cterm
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concl_of : thm -> term
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prems_of : thm -> term list
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cprems_of : thm -> cterm list
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nprems_of : thm -> int
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tpairs_of : thm -> (term*term) list
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sign_of_thm : thm -> Sign.sg
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theory_of_thm : thm -> theory
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dest_state : thm * int -> (term*term) list * term list * term * term
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wenzelm@9499
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rep_thm : thm -> \{sign_ref: Sign.sg_ref, der: bool * deriv, maxidx: int,
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paulson@8136
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shyps: sort list, hyps: term list, prop: term\}
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crep_thm : thm -> \{sign_ref: Sign.sg_ref, der: bool * deriv, maxidx: int,
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shyps: sort list, hyps: cterm list, prop:{\ts}cterm\}
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\end{ttbox}
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\begin{ttdescription}
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\item[\ttindexbold{cprop_of} $thm$] returns the statement of $thm$ as
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a certified term.
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\item[\ttindexbold{concl_of} $thm$] returns the conclusion of $thm$ as
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a term.
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\item[\ttindexbold{prems_of} $thm$] returns the premises of $thm$ as a
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list of terms.
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\item[\ttindexbold{cprems_of} $thm$] returns the premises of $thm$ as
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a list of certified terms.
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\item[\ttindexbold{nprems_of} $thm$]
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returns the number of premises in $thm$, and is equivalent to {\tt
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length~(prems_of~$thm$)}.
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|
266 |
\item[\ttindexbold{tpairs_of} $thm$] returns the flex-flex constraints
|
wenzelm@4317
|
267 |
of $thm$.
|
wenzelm@4317
|
268 |
|
wenzelm@4317
|
269 |
\item[\ttindexbold{sign_of_thm} $thm$] returns the signature
|
wenzelm@4317
|
270 |
associated with $thm$.
|
wenzelm@4317
|
271 |
|
wenzelm@4317
|
272 |
\item[\ttindexbold{theory_of_thm} $thm$] returns the theory associated
|
wenzelm@4317
|
273 |
with $thm$. Note that this does a lookup in Isabelle's global
|
wenzelm@4317
|
274 |
database of loaded theories.
|
clasohm@866
|
275 |
|
lcp@104
|
276 |
\item[\ttindexbold{dest_state} $(thm,i)$]
|
lcp@104
|
277 |
decomposes $thm$ as a tuple containing a list of flex-flex constraints, a
|
lcp@104
|
278 |
list of the subgoals~1 to~$i-1$, subgoal~$i$, and the rest of the theorem
|
lcp@104
|
279 |
(this will be an implication if there are more than $i$ subgoals).
|
lcp@104
|
280 |
|
wenzelm@4317
|
281 |
\item[\ttindexbold{rep_thm} $thm$] decomposes $thm$ as a record
|
wenzelm@4317
|
282 |
containing the statement of~$thm$ ({\tt prop}), its list of
|
wenzelm@4317
|
283 |
meta-assumptions ({\tt hyps}), its derivation ({\tt der}), a bound
|
wenzelm@4317
|
284 |
on the maximum subscript of its unknowns ({\tt maxidx}), and a
|
wenzelm@4317
|
285 |
reference to its signature ({\tt sign_ref}). The {\tt shyps} field
|
wenzelm@4317
|
286 |
is discussed below.
|
wenzelm@4317
|
287 |
|
wenzelm@4317
|
288 |
\item[\ttindexbold{crep_thm} $thm$] like \texttt{rep_thm}, but returns
|
wenzelm@4317
|
289 |
the hypotheses and statement as certified terms.
|
wenzelm@4317
|
290 |
|
lcp@326
|
291 |
\end{ttdescription}
|
lcp@104
|
292 |
|
lcp@104
|
293 |
|
wenzelm@5777
|
294 |
\subsection{*Sort hypotheses} \label{sec:sort-hyps}
|
paulson@2040
|
295 |
\index{sort hypotheses}
|
paulson@2040
|
296 |
\begin{ttbox}
|
wenzelm@7644
|
297 |
strip_shyps : thm -> thm
|
wenzelm@7644
|
298 |
strip_shyps_warning : thm -> thm
|
paulson@2040
|
299 |
\end{ttbox}
|
paulson@2040
|
300 |
|
paulson@2044
|
301 |
Isabelle's type variables are decorated with sorts, constraining them to
|
paulson@2044
|
302 |
certain ranges of types. This has little impact when sorts only serve for
|
paulson@2044
|
303 |
syntactic classification of types --- for example, FOL distinguishes between
|
paulson@2044
|
304 |
terms and other types. But when type classes are introduced through axioms,
|
paulson@2044
|
305 |
this may result in some sorts becoming {\em empty\/}: where one cannot exhibit
|
wenzelm@4317
|
306 |
a type belonging to it because certain sets of axioms are unsatisfiable.
|
paulson@2040
|
307 |
|
wenzelm@3108
|
308 |
If a theorem contains a type variable that is constrained by an empty
|
paulson@3485
|
309 |
sort, then that theorem has no instances. It is basically an instance
|
wenzelm@3108
|
310 |
of {\em ex falso quodlibet}. But what if it is used to prove another
|
wenzelm@3108
|
311 |
theorem that no longer involves that sort? The latter theorem holds
|
wenzelm@3108
|
312 |
only if under an additional non-emptiness assumption.
|
paulson@2040
|
313 |
|
paulson@3485
|
314 |
Therefore, Isabelle's theorems carry around sort hypotheses. The {\tt
|
paulson@2044
|
315 |
shyps} field is a list of sorts occurring in type variables in the current
|
paulson@2044
|
316 |
{\tt prop} and {\tt hyps} fields. It may also includes sorts used in the
|
paulson@2044
|
317 |
theorem's proof that no longer appear in the {\tt prop} or {\tt hyps}
|
paulson@3485
|
318 |
fields --- so-called {\em dangling\/} sort constraints. These are the
|
paulson@2044
|
319 |
critical ones, asserting non-emptiness of the corresponding sorts.
|
paulson@2044
|
320 |
|
wenzelm@7644
|
321 |
Isabelle automatically removes extraneous sorts from the {\tt shyps} field at
|
wenzelm@7644
|
322 |
the end of a proof, provided that non-emptiness can be established by looking
|
wenzelm@7644
|
323 |
at the theorem's signature: from the {\tt classes} and {\tt arities}
|
wenzelm@7644
|
324 |
information. This operation is performed by \texttt{strip_shyps} and
|
wenzelm@7644
|
325 |
\texttt{strip_shyps_warning}.
|
wenzelm@7644
|
326 |
|
wenzelm@7644
|
327 |
\begin{ttdescription}
|
wenzelm@7644
|
328 |
|
wenzelm@7644
|
329 |
\item[\ttindexbold{strip_shyps} $thm$] removes any extraneous sort hypotheses
|
wenzelm@7644
|
330 |
that can be witnessed from the type signature.
|
wenzelm@7644
|
331 |
|
wenzelm@7644
|
332 |
\item[\ttindexbold{strip_shyps_warning}] is like \texttt{strip_shyps}, but
|
wenzelm@7644
|
333 |
issues a warning message of any pending sort hypotheses that do not have a
|
wenzelm@7644
|
334 |
(syntactic) witness.
|
wenzelm@7644
|
335 |
|
wenzelm@7644
|
336 |
\end{ttdescription}
|
paulson@2040
|
337 |
|
paulson@2040
|
338 |
|
lcp@104
|
339 |
\subsection{Tracing flags for unification}
|
lcp@326
|
340 |
\index{tracing!of unification}
|
lcp@104
|
341 |
\begin{ttbox}
|
paulson@8136
|
342 |
Unify.trace_simp : bool ref \hfill\textbf{initially false}
|
paulson@8136
|
343 |
Unify.trace_types : bool ref \hfill\textbf{initially false}
|
paulson@8136
|
344 |
Unify.trace_bound : int ref \hfill\textbf{initially 10}
|
paulson@8136
|
345 |
Unify.search_bound : int ref \hfill\textbf{initially 20}
|
lcp@104
|
346 |
\end{ttbox}
|
lcp@104
|
347 |
Tracing the search may be useful when higher-order unification behaves
|
lcp@104
|
348 |
unexpectedly. Letting {\tt res_inst_tac} circumvent the problem is easier,
|
lcp@104
|
349 |
though.
|
lcp@326
|
350 |
\begin{ttdescription}
|
wenzelm@4317
|
351 |
\item[set Unify.trace_simp;]
|
lcp@104
|
352 |
causes tracing of the simplification phase.
|
lcp@104
|
353 |
|
wenzelm@4317
|
354 |
\item[set Unify.trace_types;]
|
lcp@104
|
355 |
generates warnings of incompleteness, when unification is not considering
|
lcp@104
|
356 |
all possible instantiations of type unknowns.
|
lcp@104
|
357 |
|
lcp@326
|
358 |
\item[Unify.trace_bound := $n$;]
|
lcp@104
|
359 |
causes unification to print tracing information once it reaches depth~$n$.
|
lcp@104
|
360 |
Use $n=0$ for full tracing. At the default value of~10, tracing
|
lcp@104
|
361 |
information is almost never printed.
|
lcp@104
|
362 |
|
paulson@8136
|
363 |
\item[Unify.search_bound := $n$;] prevents unification from
|
paulson@8136
|
364 |
searching past the depth~$n$. Because of this bound, higher-order
|
wenzelm@4317
|
365 |
unification cannot return an infinite sequence, though it can return
|
paulson@8136
|
366 |
an exponentially long one. The search rarely approaches the default value
|
wenzelm@4317
|
367 |
of~20. If the search is cut off, unification prints a warning
|
wenzelm@4317
|
368 |
\texttt{Unification bound exceeded}.
|
lcp@326
|
369 |
\end{ttdescription}
|
lcp@104
|
370 |
|
lcp@104
|
371 |
|
wenzelm@4317
|
372 |
\section{*Primitive meta-level inference rules}
|
lcp@104
|
373 |
\index{meta-rules|(}
|
wenzelm@4317
|
374 |
These implement the meta-logic in the style of the {\sc lcf} system,
|
wenzelm@4317
|
375 |
as functions from theorems to theorems. They are, rarely, useful for
|
wenzelm@4317
|
376 |
deriving results in the pure theory. Mainly, they are included for
|
wenzelm@4317
|
377 |
completeness, and most users should not bother with them. The
|
wenzelm@4317
|
378 |
meta-rules raise exception \xdx{THM} to signal malformed premises,
|
wenzelm@4317
|
379 |
incompatible signatures and similar errors.
|
lcp@104
|
380 |
|
lcp@326
|
381 |
\index{meta-assumptions}
|
lcp@104
|
382 |
The meta-logic uses natural deduction. Each theorem may depend on
|
lcp@332
|
383 |
meta-level assumptions. Certain rules, such as $({\Imp}I)$,
|
lcp@104
|
384 |
discharge assumptions; in most other rules, the conclusion depends on all
|
lcp@104
|
385 |
of the assumptions of the premises. Formally, the system works with
|
lcp@104
|
386 |
assertions of the form
|
lcp@104
|
387 |
\[ \phi \quad [\phi@1,\ldots,\phi@n], \]
|
wenzelm@3108
|
388 |
where $\phi@1$,~\ldots,~$\phi@n$ are the assumptions. This can be
|
wenzelm@3108
|
389 |
also read as a single conclusion sequent $\phi@1,\ldots,\phi@n \vdash
|
paulson@3485
|
390 |
\phi$. Do not confuse meta-level assumptions with the object-level
|
wenzelm@3108
|
391 |
assumptions in a subgoal, which are represented in the meta-logic
|
wenzelm@3108
|
392 |
using~$\Imp$.
|
lcp@104
|
393 |
|
lcp@104
|
394 |
Each theorem has a signature. Certified terms have a signature. When a
|
lcp@104
|
395 |
rule takes several premises and certified terms, it merges the signatures
|
lcp@104
|
396 |
to make a signature for the conclusion. This fails if the signatures are
|
lcp@104
|
397 |
incompatible.
|
lcp@104
|
398 |
|
wenzelm@5777
|
399 |
\medskip
|
wenzelm@5777
|
400 |
|
wenzelm@5777
|
401 |
The following presentation of primitive rules ignores sort
|
wenzelm@5777
|
402 |
hypotheses\index{sort hypotheses} (see also \S\ref{sec:sort-hyps}). These are
|
wenzelm@5777
|
403 |
handled transparently by the logic implementation.
|
wenzelm@5777
|
404 |
|
wenzelm@5777
|
405 |
\bigskip
|
wenzelm@5777
|
406 |
|
lcp@326
|
407 |
\index{meta-implication}
|
paulson@8136
|
408 |
The \textbf{implication} rules are $({\Imp}I)$
|
lcp@104
|
409 |
and $({\Imp}E)$:
|
lcp@104
|
410 |
\[ \infer[({\Imp}I)]{\phi\Imp \psi}{\infer*{\psi}{[\phi]}} \qquad
|
lcp@104
|
411 |
\infer[({\Imp}E)]{\psi}{\phi\Imp \psi & \phi} \]
|
lcp@104
|
412 |
|
lcp@326
|
413 |
\index{meta-equality}
|
lcp@104
|
414 |
Equality of truth values means logical equivalence:
|
wenzelm@3524
|
415 |
\[ \infer[({\equiv}I)]{\phi\equiv\psi}{\phi\Imp\psi &
|
wenzelm@3524
|
416 |
\psi\Imp\phi}
|
lcp@104
|
417 |
\qquad
|
lcp@104
|
418 |
\infer[({\equiv}E)]{\psi}{\phi\equiv \psi & \phi} \]
|
lcp@104
|
419 |
|
paulson@8136
|
420 |
The \textbf{equality} rules are reflexivity, symmetry, and transitivity:
|
lcp@104
|
421 |
\[ {a\equiv a}\,(refl) \qquad
|
lcp@104
|
422 |
\infer[(sym)]{b\equiv a}{a\equiv b} \qquad
|
lcp@104
|
423 |
\infer[(trans)]{a\equiv c}{a\equiv b & b\equiv c} \]
|
lcp@104
|
424 |
|
lcp@326
|
425 |
\index{lambda calc@$\lambda$-calculus}
|
lcp@104
|
426 |
The $\lambda$-conversions are $\alpha$-conversion, $\beta$-conversion, and
|
lcp@104
|
427 |
extensionality:\footnote{$\alpha$-conversion holds if $y$ is not free
|
lcp@104
|
428 |
in~$a$; $(ext)$ holds if $x$ is not free in the assumptions, $f$, or~$g$.}
|
lcp@104
|
429 |
\[ {(\lambda x.a) \equiv (\lambda y.a[y/x])} \qquad
|
lcp@104
|
430 |
{((\lambda x.a)(b)) \equiv a[b/x]} \qquad
|
lcp@104
|
431 |
\infer[(ext)]{f\equiv g}{f(x) \equiv g(x)} \]
|
lcp@104
|
432 |
|
paulson@8136
|
433 |
The \textbf{abstraction} and \textbf{combination} rules let conversions be
|
lcp@332
|
434 |
applied to subterms:\footnote{Abstraction holds if $x$ is not free in the
|
lcp@104
|
435 |
assumptions.}
|
lcp@104
|
436 |
\[ \infer[(abs)]{(\lambda x.a) \equiv (\lambda x.b)}{a\equiv b} \qquad
|
lcp@104
|
437 |
\infer[(comb)]{f(a)\equiv g(b)}{f\equiv g & a\equiv b} \]
|
lcp@104
|
438 |
|
lcp@326
|
439 |
\index{meta-quantifiers}
|
paulson@8136
|
440 |
The \textbf{universal quantification} rules are $(\Forall I)$ and $(\Forall
|
lcp@104
|
441 |
E)$:\footnote{$(\Forall I)$ holds if $x$ is not free in the assumptions.}
|
lcp@104
|
442 |
\[ \infer[(\Forall I)]{\Forall x.\phi}{\phi} \qquad
|
lcp@286
|
443 |
\infer[(\Forall E)]{\phi[b/x]}{\Forall x.\phi} \]
|
lcp@104
|
444 |
|
lcp@104
|
445 |
|
lcp@326
|
446 |
\subsection{Assumption rule}
|
lcp@326
|
447 |
\index{meta-assumptions}
|
lcp@104
|
448 |
\begin{ttbox}
|
wenzelm@3108
|
449 |
assume: cterm -> thm
|
lcp@104
|
450 |
\end{ttbox}
|
lcp@326
|
451 |
\begin{ttdescription}
|
lcp@104
|
452 |
\item[\ttindexbold{assume} $ct$]
|
lcp@332
|
453 |
makes the theorem \(\phi \;[\phi]\), where $\phi$ is the value of~$ct$.
|
lcp@104
|
454 |
The rule checks that $ct$ has type $prop$ and contains no unknowns, which
|
lcp@332
|
455 |
are not allowed in assumptions.
|
lcp@326
|
456 |
\end{ttdescription}
|
lcp@104
|
457 |
|
lcp@326
|
458 |
\subsection{Implication rules}
|
lcp@326
|
459 |
\index{meta-implication}
|
lcp@104
|
460 |
\begin{ttbox}
|
wenzelm@3108
|
461 |
implies_intr : cterm -> thm -> thm
|
wenzelm@3108
|
462 |
implies_intr_list : cterm list -> thm -> thm
|
lcp@104
|
463 |
implies_intr_hyps : thm -> thm
|
lcp@104
|
464 |
implies_elim : thm -> thm -> thm
|
lcp@104
|
465 |
implies_elim_list : thm -> thm list -> thm
|
lcp@104
|
466 |
\end{ttbox}
|
lcp@326
|
467 |
\begin{ttdescription}
|
lcp@104
|
468 |
\item[\ttindexbold{implies_intr} $ct$ $thm$]
|
lcp@104
|
469 |
is $({\Imp}I)$, where $ct$ is the assumption to discharge, say~$\phi$. It
|
lcp@332
|
470 |
maps the premise~$\psi$ to the conclusion $\phi\Imp\psi$, removing all
|
lcp@332
|
471 |
occurrences of~$\phi$ from the assumptions. The rule checks that $ct$ has
|
lcp@332
|
472 |
type $prop$.
|
lcp@104
|
473 |
|
lcp@104
|
474 |
\item[\ttindexbold{implies_intr_list} $cts$ $thm$]
|
lcp@104
|
475 |
applies $({\Imp}I)$ repeatedly, on every element of the list~$cts$.
|
lcp@104
|
476 |
|
lcp@104
|
477 |
\item[\ttindexbold{implies_intr_hyps} $thm$]
|
lcp@332
|
478 |
applies $({\Imp}I)$ to discharge all the hypotheses (assumptions) of~$thm$.
|
lcp@332
|
479 |
It maps the premise $\phi \; [\phi@1,\ldots,\phi@n]$ to the conclusion
|
lcp@104
|
480 |
$\List{\phi@1,\ldots,\phi@n}\Imp\phi$.
|
lcp@104
|
481 |
|
lcp@104
|
482 |
\item[\ttindexbold{implies_elim} $thm@1$ $thm@2$]
|
lcp@104
|
483 |
applies $({\Imp}E)$ to $thm@1$ and~$thm@2$. It maps the premises $\phi\Imp
|
lcp@104
|
484 |
\psi$ and $\phi$ to the conclusion~$\psi$.
|
lcp@104
|
485 |
|
lcp@104
|
486 |
\item[\ttindexbold{implies_elim_list} $thm$ $thms$]
|
lcp@104
|
487 |
applies $({\Imp}E)$ repeatedly to $thm$, using each element of~$thms$ in
|
wenzelm@151
|
488 |
turn. It maps the premises $\List{\phi@1,\ldots,\phi@n}\Imp\psi$ and
|
lcp@104
|
489 |
$\phi@1$,\ldots,$\phi@n$ to the conclusion~$\psi$.
|
lcp@326
|
490 |
\end{ttdescription}
|
lcp@104
|
491 |
|
lcp@326
|
492 |
\subsection{Logical equivalence rules}
|
lcp@326
|
493 |
\index{meta-equality}
|
lcp@104
|
494 |
\begin{ttbox}
|
lcp@326
|
495 |
equal_intr : thm -> thm -> thm
|
lcp@326
|
496 |
equal_elim : thm -> thm -> thm
|
lcp@104
|
497 |
\end{ttbox}
|
lcp@326
|
498 |
\begin{ttdescription}
|
lcp@104
|
499 |
\item[\ttindexbold{equal_intr} $thm@1$ $thm@2$]
|
lcp@332
|
500 |
applies $({\equiv}I)$ to $thm@1$ and~$thm@2$. It maps the premises~$\psi$
|
lcp@332
|
501 |
and~$\phi$ to the conclusion~$\phi\equiv\psi$; the assumptions are those of
|
lcp@332
|
502 |
the first premise with~$\phi$ removed, plus those of
|
lcp@332
|
503 |
the second premise with~$\psi$ removed.
|
lcp@104
|
504 |
|
lcp@104
|
505 |
\item[\ttindexbold{equal_elim} $thm@1$ $thm@2$]
|
lcp@104
|
506 |
applies $({\equiv}E)$ to $thm@1$ and~$thm@2$. It maps the premises
|
lcp@104
|
507 |
$\phi\equiv\psi$ and $\phi$ to the conclusion~$\psi$.
|
lcp@326
|
508 |
\end{ttdescription}
|
lcp@104
|
509 |
|
lcp@104
|
510 |
|
lcp@104
|
511 |
\subsection{Equality rules}
|
lcp@326
|
512 |
\index{meta-equality}
|
lcp@104
|
513 |
\begin{ttbox}
|
wenzelm@3108
|
514 |
reflexive : cterm -> thm
|
lcp@104
|
515 |
symmetric : thm -> thm
|
lcp@104
|
516 |
transitive : thm -> thm -> thm
|
lcp@104
|
517 |
\end{ttbox}
|
lcp@326
|
518 |
\begin{ttdescription}
|
lcp@104
|
519 |
\item[\ttindexbold{reflexive} $ct$]
|
wenzelm@151
|
520 |
makes the theorem \(ct\equiv ct\).
|
lcp@104
|
521 |
|
lcp@104
|
522 |
\item[\ttindexbold{symmetric} $thm$]
|
lcp@104
|
523 |
maps the premise $a\equiv b$ to the conclusion $b\equiv a$.
|
lcp@104
|
524 |
|
lcp@104
|
525 |
\item[\ttindexbold{transitive} $thm@1$ $thm@2$]
|
lcp@104
|
526 |
maps the premises $a\equiv b$ and $b\equiv c$ to the conclusion~${a\equiv c}$.
|
lcp@326
|
527 |
\end{ttdescription}
|
lcp@104
|
528 |
|
lcp@104
|
529 |
|
lcp@104
|
530 |
\subsection{The $\lambda$-conversion rules}
|
lcp@326
|
531 |
\index{lambda calc@$\lambda$-calculus}
|
lcp@104
|
532 |
\begin{ttbox}
|
wenzelm@3108
|
533 |
beta_conversion : cterm -> thm
|
lcp@104
|
534 |
extensional : thm -> thm
|
wenzelm@3108
|
535 |
abstract_rule : string -> cterm -> thm -> thm
|
lcp@104
|
536 |
combination : thm -> thm -> thm
|
lcp@104
|
537 |
\end{ttbox}
|
lcp@326
|
538 |
There is no rule for $\alpha$-conversion because Isabelle regards
|
lcp@326
|
539 |
$\alpha$-convertible theorems as equal.
|
lcp@326
|
540 |
\begin{ttdescription}
|
lcp@104
|
541 |
\item[\ttindexbold{beta_conversion} $ct$]
|
lcp@104
|
542 |
makes the theorem $((\lambda x.a)(b)) \equiv a[b/x]$, where $ct$ is the
|
lcp@104
|
543 |
term $(\lambda x.a)(b)$.
|
lcp@104
|
544 |
|
lcp@104
|
545 |
\item[\ttindexbold{extensional} $thm$]
|
lcp@104
|
546 |
maps the premise $f(x) \equiv g(x)$ to the conclusion $f\equiv g$.
|
lcp@104
|
547 |
Parameter~$x$ is taken from the premise. It may be an unknown or a free
|
lcp@332
|
548 |
variable (provided it does not occur in the assumptions); it must not occur
|
lcp@104
|
549 |
in $f$ or~$g$.
|
lcp@104
|
550 |
|
lcp@104
|
551 |
\item[\ttindexbold{abstract_rule} $v$ $x$ $thm$]
|
lcp@104
|
552 |
maps the premise $a\equiv b$ to the conclusion $(\lambda x.a) \equiv
|
lcp@104
|
553 |
(\lambda x.b)$, abstracting over all occurrences (if any!) of~$x$.
|
lcp@104
|
554 |
Parameter~$x$ is supplied as a cterm. It may be an unknown or a free
|
lcp@332
|
555 |
variable (provided it does not occur in the assumptions). In the
|
lcp@104
|
556 |
conclusion, the bound variable is named~$v$.
|
lcp@104
|
557 |
|
lcp@104
|
558 |
\item[\ttindexbold{combination} $thm@1$ $thm@2$]
|
lcp@104
|
559 |
maps the premises $f\equiv g$ and $a\equiv b$ to the conclusion~$f(a)\equiv
|
lcp@104
|
560 |
g(b)$.
|
lcp@326
|
561 |
\end{ttdescription}
|
lcp@104
|
562 |
|
lcp@104
|
563 |
|
lcp@326
|
564 |
\subsection{Forall introduction rules}
|
lcp@326
|
565 |
\index{meta-quantifiers}
|
lcp@104
|
566 |
\begin{ttbox}
|
wenzelm@3108
|
567 |
forall_intr : cterm -> thm -> thm
|
wenzelm@3108
|
568 |
forall_intr_list : cterm list -> thm -> thm
|
wenzelm@3108
|
569 |
forall_intr_frees : thm -> thm
|
lcp@104
|
570 |
\end{ttbox}
|
lcp@104
|
571 |
|
lcp@326
|
572 |
\begin{ttdescription}
|
lcp@104
|
573 |
\item[\ttindexbold{forall_intr} $x$ $thm$]
|
lcp@104
|
574 |
applies $({\Forall}I)$, abstracting over all occurrences (if any!) of~$x$.
|
lcp@104
|
575 |
The rule maps the premise $\phi$ to the conclusion $\Forall x.\phi$.
|
lcp@104
|
576 |
Parameter~$x$ is supplied as a cterm. It may be an unknown or a free
|
lcp@332
|
577 |
variable (provided it does not occur in the assumptions).
|
lcp@104
|
578 |
|
lcp@104
|
579 |
\item[\ttindexbold{forall_intr_list} $xs$ $thm$]
|
lcp@104
|
580 |
applies $({\Forall}I)$ repeatedly, on every element of the list~$xs$.
|
lcp@104
|
581 |
|
lcp@104
|
582 |
\item[\ttindexbold{forall_intr_frees} $thm$]
|
lcp@104
|
583 |
applies $({\Forall}I)$ repeatedly, generalizing over all the free variables
|
lcp@104
|
584 |
of the premise.
|
lcp@326
|
585 |
\end{ttdescription}
|
lcp@104
|
586 |
|
lcp@104
|
587 |
|
lcp@326
|
588 |
\subsection{Forall elimination rules}
|
lcp@104
|
589 |
\begin{ttbox}
|
wenzelm@3108
|
590 |
forall_elim : cterm -> thm -> thm
|
wenzelm@3108
|
591 |
forall_elim_list : cterm list -> thm -> thm
|
wenzelm@3108
|
592 |
forall_elim_var : int -> thm -> thm
|
wenzelm@3108
|
593 |
forall_elim_vars : int -> thm -> thm
|
lcp@104
|
594 |
\end{ttbox}
|
lcp@104
|
595 |
|
lcp@326
|
596 |
\begin{ttdescription}
|
lcp@104
|
597 |
\item[\ttindexbold{forall_elim} $ct$ $thm$]
|
lcp@104
|
598 |
applies $({\Forall}E)$, mapping the premise $\Forall x.\phi$ to the conclusion
|
lcp@104
|
599 |
$\phi[ct/x]$. The rule checks that $ct$ and $x$ have the same type.
|
lcp@104
|
600 |
|
lcp@104
|
601 |
\item[\ttindexbold{forall_elim_list} $cts$ $thm$]
|
lcp@104
|
602 |
applies $({\Forall}E)$ repeatedly, on every element of the list~$cts$.
|
lcp@104
|
603 |
|
lcp@104
|
604 |
\item[\ttindexbold{forall_elim_var} $k$ $thm$]
|
lcp@104
|
605 |
applies $({\Forall}E)$, mapping the premise $\Forall x.\phi$ to the conclusion
|
lcp@104
|
606 |
$\phi[\Var{x@k}/x]$. Thus, it replaces the outermost $\Forall$-bound
|
lcp@104
|
607 |
variable by an unknown having subscript~$k$.
|
lcp@104
|
608 |
|
paulson@9258
|
609 |
\item[\ttindexbold{forall_elim_vars} $k$ $thm$]
|
paulson@9258
|
610 |
applies {\tt forall_elim_var}~$k$ repeatedly until the theorem no longer has
|
paulson@9258
|
611 |
the form $\Forall x.\phi$.
|
lcp@326
|
612 |
\end{ttdescription}
|
lcp@104
|
613 |
|
paulson@8135
|
614 |
|
lcp@326
|
615 |
\subsection{Instantiation of unknowns}
|
lcp@326
|
616 |
\index{instantiation}
|
paulson@8136
|
617 |
\begin{alltt}\footnotesize
|
wenzelm@3135
|
618 |
instantiate: (indexname * ctyp){\thinspace}list * (cterm * cterm){\thinspace}list -> thm -> thm
|
paulson@8136
|
619 |
\end{alltt}
|
paulson@8135
|
620 |
There are two versions of this rule. The primitive one is
|
paulson@8135
|
621 |
\ttindexbold{Thm.instantiate}, which merely performs the instantiation and can
|
paulson@8135
|
622 |
produce a conclusion not in normal form. A derived version is
|
paulson@8135
|
623 |
\ttindexbold{Drule.instantiate}, which normalizes its conclusion.
|
paulson@8135
|
624 |
|
lcp@326
|
625 |
\begin{ttdescription}
|
paulson@8136
|
626 |
\item[\ttindexbold{instantiate} ($tyinsts$,$insts$) $thm$]
|
lcp@326
|
627 |
simultaneously substitutes types for type unknowns (the
|
lcp@104
|
628 |
$tyinsts$) and terms for term unknowns (the $insts$). Instantiations are
|
lcp@104
|
629 |
given as $(v,t)$ pairs, where $v$ is an unknown and $t$ is a term (of the
|
lcp@104
|
630 |
same type as $v$) or a type (of the same sort as~$v$). All the unknowns
|
paulson@8135
|
631 |
must be distinct.
|
wenzelm@4376
|
632 |
|
paulson@8135
|
633 |
In some cases, \ttindex{instantiate'} (see \S\ref{sec:instantiate})
|
wenzelm@4376
|
634 |
provides a more convenient interface to this rule.
|
lcp@326
|
635 |
\end{ttdescription}
|
lcp@104
|
636 |
|
lcp@104
|
637 |
|
paulson@8135
|
638 |
|
paulson@8135
|
639 |
|
lcp@326
|
640 |
\subsection{Freezing/thawing type unknowns}
|
lcp@326
|
641 |
\index{type unknowns!freezing/thawing of}
|
lcp@104
|
642 |
\begin{ttbox}
|
lcp@104
|
643 |
freezeT: thm -> thm
|
lcp@104
|
644 |
varifyT: thm -> thm
|
lcp@104
|
645 |
\end{ttbox}
|
lcp@326
|
646 |
\begin{ttdescription}
|
lcp@104
|
647 |
\item[\ttindexbold{freezeT} $thm$]
|
lcp@104
|
648 |
converts all the type unknowns in $thm$ to free type variables.
|
lcp@104
|
649 |
|
lcp@104
|
650 |
\item[\ttindexbold{varifyT} $thm$]
|
lcp@104
|
651 |
converts all the free type variables in $thm$ to type unknowns.
|
lcp@326
|
652 |
\end{ttdescription}
|
lcp@104
|
653 |
|
lcp@104
|
654 |
|
lcp@104
|
655 |
\section{Derived rules for goal-directed proof}
|
lcp@104
|
656 |
Most of these rules have the sole purpose of implementing particular
|
lcp@104
|
657 |
tactics. There are few occasions for applying them directly to a theorem.
|
lcp@104
|
658 |
|
lcp@104
|
659 |
\subsection{Proof by assumption}
|
lcp@326
|
660 |
\index{meta-assumptions}
|
lcp@104
|
661 |
\begin{ttbox}
|
wenzelm@4276
|
662 |
assumption : int -> thm -> thm Seq.seq
|
lcp@104
|
663 |
eq_assumption : int -> thm -> thm
|
lcp@104
|
664 |
\end{ttbox}
|
lcp@326
|
665 |
\begin{ttdescription}
|
lcp@104
|
666 |
\item[\ttindexbold{assumption} {\it i} $thm$]
|
lcp@104
|
667 |
attempts to solve premise~$i$ of~$thm$ by assumption.
|
lcp@104
|
668 |
|
lcp@104
|
669 |
\item[\ttindexbold{eq_assumption}]
|
lcp@104
|
670 |
is like {\tt assumption} but does not use unification.
|
lcp@326
|
671 |
\end{ttdescription}
|
lcp@104
|
672 |
|
lcp@104
|
673 |
|
lcp@104
|
674 |
\subsection{Resolution}
|
lcp@326
|
675 |
\index{resolution}
|
lcp@104
|
676 |
\begin{ttbox}
|
lcp@104
|
677 |
biresolution : bool -> (bool*thm)list -> int -> thm
|
wenzelm@4276
|
678 |
-> thm Seq.seq
|
lcp@104
|
679 |
\end{ttbox}
|
lcp@326
|
680 |
\begin{ttdescription}
|
lcp@104
|
681 |
\item[\ttindexbold{biresolution} $match$ $rules$ $i$ $state$]
|
lcp@326
|
682 |
performs bi-resolution on subgoal~$i$ of $state$, using the list of $\it
|
lcp@104
|
683 |
(flag,rule)$ pairs. For each pair, it applies resolution if the flag
|
lcp@104
|
684 |
is~{\tt false} and elim-resolution if the flag is~{\tt true}. If $match$
|
lcp@104
|
685 |
is~{\tt true}, the $state$ is not instantiated.
|
lcp@326
|
686 |
\end{ttdescription}
|
lcp@104
|
687 |
|
lcp@104
|
688 |
|
lcp@104
|
689 |
\subsection{Composition: resolution without lifting}
|
lcp@326
|
690 |
\index{resolution!without lifting}
|
lcp@104
|
691 |
\begin{ttbox}
|
lcp@104
|
692 |
compose : thm * int * thm -> thm list
|
lcp@104
|
693 |
COMP : thm * thm -> thm
|
lcp@104
|
694 |
bicompose : bool -> bool * thm * int -> int -> thm
|
wenzelm@4276
|
695 |
-> thm Seq.seq
|
lcp@104
|
696 |
\end{ttbox}
|
lcp@104
|
697 |
In forward proof, a typical use of composition is to regard an assertion of
|
lcp@104
|
698 |
the form $\phi\Imp\psi$ as atomic. Schematic variables are not renamed, so
|
lcp@104
|
699 |
beware of clashes!
|
lcp@326
|
700 |
\begin{ttdescription}
|
lcp@104
|
701 |
\item[\ttindexbold{compose} ($thm@1$, $i$, $thm@2$)]
|
lcp@104
|
702 |
uses $thm@1$, regarded as an atomic formula, to solve premise~$i$
|
lcp@104
|
703 |
of~$thm@2$. Let $thm@1$ and $thm@2$ be $\psi$ and $\List{\phi@1; \ldots;
|
lcp@104
|
704 |
\phi@n} \Imp \phi$. For each $s$ that unifies~$\psi$ and $\phi@i$, the
|
lcp@104
|
705 |
result list contains the theorem
|
lcp@104
|
706 |
\[ (\List{\phi@1; \ldots; \phi@{i-1}; \phi@{i+1}; \ldots; \phi@n} \Imp \phi)s.
|
lcp@104
|
707 |
\]
|
lcp@104
|
708 |
|
lcp@1119
|
709 |
\item[$thm@1$ \ttindexbold{COMP} $thm@2$]
|
lcp@104
|
710 |
calls \hbox{\tt compose ($thm@1$, 1, $thm@2$)} and returns the result, if
|
lcp@326
|
711 |
unique; otherwise, it raises exception~\xdx{THM}\@. It is
|
lcp@104
|
712 |
analogous to {\tt RS}\@.
|
lcp@104
|
713 |
|
lcp@104
|
714 |
For example, suppose that $thm@1$ is $a=b\Imp b=a$, a symmetry rule, and
|
lcp@332
|
715 |
that $thm@2$ is $\List{P\Imp Q; \neg Q} \Imp\neg P$, which is the
|
lcp@104
|
716 |
principle of contrapositives. Then the result would be the
|
lcp@104
|
717 |
derived rule $\neg(b=a)\Imp\neg(a=b)$.
|
lcp@104
|
718 |
|
lcp@104
|
719 |
\item[\ttindexbold{bicompose} $match$ ($flag$, $rule$, $m$) $i$ $state$]
|
lcp@104
|
720 |
refines subgoal~$i$ of $state$ using $rule$, without lifting. The $rule$
|
lcp@104
|
721 |
is taken to have the form $\List{\psi@1; \ldots; \psi@m} \Imp \psi$, where
|
lcp@326
|
722 |
$\psi$ need not be atomic; thus $m$ determines the number of new
|
lcp@104
|
723 |
subgoals. If $flag$ is {\tt true} then it performs elim-resolution --- it
|
lcp@104
|
724 |
solves the first premise of~$rule$ by assumption and deletes that
|
lcp@104
|
725 |
assumption. If $match$ is~{\tt true}, the $state$ is not instantiated.
|
lcp@326
|
726 |
\end{ttdescription}
|
lcp@104
|
727 |
|
lcp@104
|
728 |
|
lcp@104
|
729 |
\subsection{Other meta-rules}
|
lcp@104
|
730 |
\begin{ttbox}
|
wenzelm@3108
|
731 |
trivial : cterm -> thm
|
lcp@104
|
732 |
lift_rule : (thm * int) -> thm -> thm
|
lcp@104
|
733 |
rename_params_rule : string list * int -> thm -> thm
|
wenzelm@4276
|
734 |
flexflex_rule : thm -> thm Seq.seq
|
lcp@104
|
735 |
\end{ttbox}
|
lcp@326
|
736 |
\begin{ttdescription}
|
lcp@104
|
737 |
\item[\ttindexbold{trivial} $ct$]
|
lcp@104
|
738 |
makes the theorem \(\phi\Imp\phi\), where $\phi$ is the value of~$ct$.
|
lcp@104
|
739 |
This is the initial state for a goal-directed proof of~$\phi$. The rule
|
lcp@104
|
740 |
checks that $ct$ has type~$prop$.
|
lcp@104
|
741 |
|
lcp@104
|
742 |
\item[\ttindexbold{lift_rule} ($state$, $i$) $rule$] \index{lifting}
|
lcp@104
|
743 |
prepares $rule$ for resolution by lifting it over the parameters and
|
lcp@104
|
744 |
assumptions of subgoal~$i$ of~$state$.
|
lcp@104
|
745 |
|
lcp@104
|
746 |
\item[\ttindexbold{rename_params_rule} ({\it names}, {\it i}) $thm$]
|
lcp@104
|
747 |
uses the $names$ to rename the parameters of premise~$i$ of $thm$. The
|
lcp@104
|
748 |
names must be distinct. If there are fewer names than parameters, then the
|
lcp@104
|
749 |
rule renames the innermost parameters and may modify the remaining ones to
|
lcp@104
|
750 |
ensure that all the parameters are distinct.
|
lcp@104
|
751 |
\index{parameters!renaming}
|
lcp@104
|
752 |
|
lcp@104
|
753 |
\item[\ttindexbold{flexflex_rule} $thm$] \index{flex-flex constraints}
|
lcp@104
|
754 |
removes all flex-flex pairs from $thm$ using the trivial unifier.
|
lcp@326
|
755 |
\end{ttdescription}
|
paulson@1590
|
756 |
\index{meta-rules|)}
|
paulson@1590
|
757 |
|
paulson@1590
|
758 |
|
berghofe@11622
|
759 |
\section{Proof terms}\label{sec:proofObjects}
|
berghofe@11622
|
760 |
\index{proof terms|(} Isabelle can record the full meta-level proof of each
|
berghofe@11622
|
761 |
theorem. The proof term contains all logical inferences in detail.
|
berghofe@11622
|
762 |
%while
|
berghofe@11622
|
763 |
%omitting bookkeeping steps that have no logical meaning to an outside
|
berghofe@11622
|
764 |
%observer. Rewriting steps are recorded in similar detail as the output of
|
berghofe@11622
|
765 |
%simplifier tracing.
|
berghofe@11622
|
766 |
Resolution and rewriting steps are broken down to primitive rules of the
|
berghofe@11622
|
767 |
meta-logic. The proof term can be inspected by a separate proof-checker,
|
berghofe@11622
|
768 |
for example.
|
paulson@1590
|
769 |
|
berghofe@11622
|
770 |
According to the well-known {\em Curry-Howard isomorphism}, a proof can
|
berghofe@11622
|
771 |
be viewed as a $\lambda$-term. Following this idea, proofs
|
berghofe@11622
|
772 |
in Isabelle are internally represented by a datatype similar to the one for
|
berghofe@11622
|
773 |
terms described in \S\ref{sec:terms}.
|
berghofe@11622
|
774 |
\begin{ttbox}
|
berghofe@11622
|
775 |
infix 8 % %%;
|
paulson@1590
|
776 |
|
berghofe@11622
|
777 |
datatype proof =
|
berghofe@11622
|
778 |
PBound of int
|
berghofe@11622
|
779 |
| Abst of string * typ option * proof
|
berghofe@11622
|
780 |
| AbsP of string * term option * proof
|
berghofe@11622
|
781 |
| op % of proof * term option
|
berghofe@11622
|
782 |
| op %% of proof * proof
|
berghofe@11622
|
783 |
| Hyp of term
|
berghofe@11622
|
784 |
| PThm of (string * (string * string list) list) *
|
berghofe@11622
|
785 |
proof * term * typ list option
|
berghofe@11622
|
786 |
| PAxm of string * term * typ list option
|
berghofe@11622
|
787 |
| Oracle of string * term * typ list option
|
berghofe@11622
|
788 |
| MinProof of proof list;
|
berghofe@11622
|
789 |
\end{ttbox}
|
paulson@1590
|
790 |
|
berghofe@11622
|
791 |
\begin{ttdescription}
|
berghofe@11622
|
792 |
\item[\ttindexbold{Abst} ($a$, $\tau$, $prf$)] is the abstraction over
|
berghofe@11622
|
793 |
a {\it term variable} of type $\tau$ in the body $prf$. Logically, this
|
berghofe@11622
|
794 |
corresponds to $\bigwedge$ introduction. The name $a$ is used only for
|
berghofe@11622
|
795 |
parsing and printing.
|
berghofe@11622
|
796 |
\item[\ttindexbold{AbsP} ($a$, $\varphi$, $prf$)] is the abstraction
|
berghofe@11622
|
797 |
over a {\it proof variable} standing for a proof of proposition $\varphi$
|
berghofe@11622
|
798 |
in the body $prf$. This corresponds to $\Longrightarrow$ introduction.
|
berghofe@11622
|
799 |
\item[$prf$ \% $t$] \index{\%@{\tt\%}|bold}
|
berghofe@11622
|
800 |
is the application of proof $prf$ to term $t$
|
berghofe@11622
|
801 |
which corresponds to $\bigwedge$ elimination.
|
berghofe@11622
|
802 |
\item[$prf@1$ \%\% $prf@2$] \index{\%\%@{\tt\%\%}|bold}
|
berghofe@11622
|
803 |
is the application of proof $prf@1$ to
|
berghofe@11622
|
804 |
proof $prf@2$ which corresponds to $\Longrightarrow$ elimination.
|
berghofe@11622
|
805 |
\item[\ttindexbold{PBound} $i$] is a {\em proof variable} with de Bruijn
|
berghofe@11622
|
806 |
\cite{debruijn72} index $i$.
|
berghofe@11622
|
807 |
\item[\ttindexbold{Hyp} $\varphi$] corresponds to the use of a meta level
|
berghofe@11622
|
808 |
hypothesis $\varphi$.
|
berghofe@11622
|
809 |
\item[\ttindexbold{PThm} (($name$, $tags$), $prf$, $\varphi$, $\overline{\tau}$)]
|
berghofe@11622
|
810 |
stands for a pre-proved theorem, where $name$ is the name of the theorem,
|
berghofe@11622
|
811 |
$prf$ is its actual proof, $\varphi$ is the proven proposition,
|
berghofe@11622
|
812 |
and $\overline{\tau}$ is
|
berghofe@11622
|
813 |
a type assignment for the type variables occurring in the proposition.
|
berghofe@11622
|
814 |
\item[\ttindexbold{PAxm} ($name$, $\varphi$, $\overline{\tau}$)]
|
berghofe@11622
|
815 |
corresponds to the use of an axiom with name $name$ and proposition
|
berghofe@11622
|
816 |
$\varphi$, where $\overline{\tau}$ is a type assignment for the type
|
berghofe@11622
|
817 |
variables occurring in the proposition.
|
berghofe@11622
|
818 |
\item[\ttindexbold{Oracle} ($name$, $\varphi$, $\overline{\tau}$)]
|
berghofe@11622
|
819 |
denotes the invocation of an oracle with name $name$ which produced
|
berghofe@11622
|
820 |
a proposition $\varphi$, where $\overline{\tau}$ is a type assignment
|
berghofe@11622
|
821 |
for the type variables occurring in the proposition.
|
berghofe@11622
|
822 |
\item[\ttindexbold{MinProof} $prfs$]
|
berghofe@11622
|
823 |
represents a {\em minimal proof} where $prfs$ is a list of theorems,
|
berghofe@11622
|
824 |
axioms or oracles.
|
berghofe@11622
|
825 |
\end{ttdescription}
|
berghofe@11622
|
826 |
Note that there are no separate constructors
|
berghofe@11622
|
827 |
for abstraction and application on the level of {\em types}, since
|
berghofe@11622
|
828 |
instantiation of type variables is accomplished via the type assignments
|
berghofe@11622
|
829 |
attached to {\tt Thm}, {\tt Axm} and {\tt Oracle}.
|
berghofe@11622
|
830 |
|
paulson@1590
|
831 |
Each theorem's derivation is stored as the {\tt der} field of its internal
|
paulson@1590
|
832 |
record:
|
paulson@1590
|
833 |
\begin{ttbox}
|
berghofe@11622
|
834 |
#2 (#der (rep_thm conjI));
|
berghofe@11622
|
835 |
{\out PThm (("HOL.conjI", []),}
|
berghofe@11622
|
836 |
{\out AbsP ("H", None, AbsP ("H", None, \dots)), \dots, None) %}
|
berghofe@11622
|
837 |
{\out None % None : Proofterm.proof}
|
paulson@1590
|
838 |
\end{ttbox}
|
berghofe@11622
|
839 |
This proof term identifies a labelled theorem, {\tt conjI} of theory
|
berghofe@11622
|
840 |
\texttt{HOL}, whose underlying proof is
|
berghofe@11622
|
841 |
{\tt AbsP ("H", None, AbsP ("H", None, $\dots$))}.
|
berghofe@11622
|
842 |
The theorem is applied to two (implicit) term arguments, which correspond
|
berghofe@11622
|
843 |
to the two variables occurring in its proposition.
|
paulson@1590
|
844 |
|
berghofe@11622
|
845 |
Isabelle's inference kernel can produce proof objects with different
|
berghofe@11622
|
846 |
levels of detail. This is controlled via the global reference variable
|
berghofe@11622
|
847 |
\ttindexbold{proofs}:
|
paulson@1590
|
848 |
\begin{ttdescription}
|
berghofe@11622
|
849 |
\item[proofs := 0;] only record uses of oracles
|
berghofe@11622
|
850 |
\item[proofs := 1;] record uses of oracles as well as dependencies
|
berghofe@11622
|
851 |
on other theorems and axioms
|
berghofe@11622
|
852 |
\item[proofs := 2;] record inferences in full detail
|
paulson@1590
|
853 |
\end{ttdescription}
|
berghofe@11622
|
854 |
Reconstruction and checking of proofs as described in \S\ref{sec:reconstruct_proofs}
|
berghofe@11622
|
855 |
will not work for proofs constructed with {\tt proofs} set to
|
berghofe@11622
|
856 |
{\tt 0} or {\tt 1}.
|
berghofe@11622
|
857 |
Theorems involving oracles will be printed with a
|
berghofe@11622
|
858 |
suffixed \verb|[!]| to point out the different quality of confidence achieved.
|
wenzelm@5371
|
859 |
|
berghofe@7871
|
860 |
\medskip
|
berghofe@7871
|
861 |
|
berghofe@11622
|
862 |
The dependencies of theorems can be viewed using the function
|
berghofe@11622
|
863 |
\ttindexbold{thm_deps}\index{theorems!dependencies}:
|
berghofe@7871
|
864 |
\begin{ttbox}
|
berghofe@7871
|
865 |
thm_deps [\(thm@1\), \(\ldots\), \(thm@n\)];
|
berghofe@7871
|
866 |
\end{ttbox}
|
berghofe@7871
|
867 |
generates the dependency graph of the theorems $thm@1$, $\ldots$, $thm@n$ and
|
berghofe@11622
|
868 |
displays it using Isabelle's graph browser. For this to work properly,
|
berghofe@11622
|
869 |
the theorems in question have to be proved with {\tt proofs} set to a value
|
berghofe@11622
|
870 |
greater than {\tt 0}. You can use
|
berghofe@7871
|
871 |
\begin{ttbox}
|
berghofe@11622
|
872 |
ThmDeps.enable : unit -> unit
|
berghofe@11622
|
873 |
ThmDeps.disable : unit -> unit
|
berghofe@7871
|
874 |
\end{ttbox}
|
berghofe@11622
|
875 |
to set \texttt{proofs} appropriately.
|
berghofe@11622
|
876 |
|
berghofe@11622
|
877 |
\subsection{Reconstructing and checking proof terms}\label{sec:reconstruct_proofs}
|
berghofe@11622
|
878 |
\index{proof terms!reconstructing}
|
berghofe@11622
|
879 |
\index{proof terms!checking}
|
berghofe@11622
|
880 |
|
berghofe@11622
|
881 |
When looking at the above datatype of proofs more closely, one notices that
|
berghofe@11622
|
882 |
some arguments of constructors are {\it optional}. The reason for this is that
|
berghofe@11622
|
883 |
keeping a full proof term for each theorem would result in enormous memory
|
berghofe@11622
|
884 |
requirements. Fortunately, typical proof terms usually contain quite a lot of
|
berghofe@11622
|
885 |
redundant information that can be reconstructed from the context. Therefore,
|
berghofe@11622
|
886 |
Isabelle's inference kernel creates only {\em partial} (or {\em implicit})
|
berghofe@11622
|
887 |
\index{proof terms!partial} proof terms, in which
|
berghofe@11622
|
888 |
all typing information in terms, all term and type labels of abstractions
|
berghofe@11622
|
889 |
{\tt AbsP} and {\tt Abst}, and (if possible) some argument terms of
|
berghofe@11622
|
890 |
\verb!%! are omitted. The following functions are available for
|
berghofe@11622
|
891 |
reconstructing and checking proof terms:
|
berghofe@11622
|
892 |
\begin{ttbox}
|
berghofe@11622
|
893 |
Reconstruct.reconstruct_proof :
|
berghofe@11622
|
894 |
Sign.sg -> term -> Proofterm.proof -> Proofterm.proof
|
berghofe@11622
|
895 |
Reconstruct.expand_proof :
|
berghofe@11622
|
896 |
Sign.sg -> string list -> Proofterm.proof -> Proofterm.proof
|
berghofe@11622
|
897 |
ProofChecker.thm_of_proof : theory -> Proofterm.proof -> thm
|
berghofe@11622
|
898 |
\end{ttbox}
|
berghofe@11622
|
899 |
|
berghofe@11622
|
900 |
\begin{ttdescription}
|
berghofe@11622
|
901 |
\item[Reconstruct.reconstruct_proof $sg$ $t$ $prf$]
|
berghofe@11622
|
902 |
turns the partial proof $prf$ into a full proof of the
|
berghofe@11622
|
903 |
proposition denoted by $t$, with respect to signature $sg$.
|
berghofe@11622
|
904 |
Reconstruction will fail with an error message if $prf$
|
berghofe@11622
|
905 |
is not a proof of $t$, is ill-formed, or does not contain
|
berghofe@11622
|
906 |
sufficient information for reconstruction by
|
berghofe@11622
|
907 |
{\em higher order pattern unification}
|
berghofe@11622
|
908 |
\cite{nipkow-patterns, Berghofer-Nipkow:2000:TPHOL}.
|
berghofe@11622
|
909 |
The latter may only happen for proofs
|
berghofe@11622
|
910 |
built up ``by hand'' but not for those produced automatically
|
berghofe@11622
|
911 |
by Isabelle's inference kernel.
|
berghofe@11622
|
912 |
\item[Reconstruct.expand_proof $sg$
|
berghofe@11622
|
913 |
\ttlbrack$name@1$, $\ldots$, $name@n${\ttrbrack} $prf$]
|
berghofe@11622
|
914 |
expands and reconstructs the proofs of all theorems with names
|
berghofe@11622
|
915 |
$name@1$, $\ldots$, $name@n$ in the (full) proof $prf$.
|
berghofe@11622
|
916 |
\item[ProofChecker.thm_of_proof $thy$ $prf$] turns the (full) proof
|
berghofe@11622
|
917 |
$prf$ into a theorem with respect to theory $thy$ by replaying
|
berghofe@11622
|
918 |
it using only primitive rules from Isabelle's inference kernel.
|
berghofe@11622
|
919 |
\end{ttdescription}
|
berghofe@11622
|
920 |
|
berghofe@11622
|
921 |
\subsection{Parsing and printing proof terms}
|
berghofe@11622
|
922 |
\index{proof terms!parsing}
|
berghofe@11622
|
923 |
\index{proof terms!printing}
|
berghofe@11622
|
924 |
|
berghofe@11622
|
925 |
Isabelle offers several functions for parsing and printing
|
berghofe@11622
|
926 |
proof terms. The concrete syntax for proof terms is described
|
berghofe@11622
|
927 |
in Fig.\ts\ref{fig:proof_gram}.
|
berghofe@11622
|
928 |
Implicit term arguments in partial proofs are indicated
|
berghofe@11622
|
929 |
by ``{\tt _}''.
|
berghofe@11622
|
930 |
Type arguments for theorems and axioms may be specified using
|
berghofe@11622
|
931 |
\verb!%! or ``$\cdot$'' with an argument of the form {\tt TYPE($type$)}
|
berghofe@11622
|
932 |
(see \S\ref{sec:basic_syntax}).
|
berghofe@11622
|
933 |
They must appear before any other term argument of a theorem
|
berghofe@11622
|
934 |
or axiom. In contrast to term arguments, type arguments may
|
berghofe@11622
|
935 |
be completely omitted.
|
berghofe@11622
|
936 |
\begin{ttbox}
|
berghofe@11625
|
937 |
ProofSyntax.read_proof : theory -> bool -> string -> Proofterm.proof
|
berghofe@11625
|
938 |
ProofSyntax.pretty_proof : Sign.sg -> Proofterm.proof -> Pretty.T
|
berghofe@11625
|
939 |
ProofSyntax.pretty_proof_of : bool -> thm -> Pretty.T
|
berghofe@11625
|
940 |
ProofSyntax.print_proof_of : bool -> thm -> unit
|
berghofe@11622
|
941 |
\end{ttbox}
|
berghofe@11622
|
942 |
\begin{figure}
|
berghofe@11622
|
943 |
\begin{center}
|
berghofe@11622
|
944 |
\begin{tabular}{rcl}
|
berghofe@11622
|
945 |
$proof$ & $=$ & {\tt Lam} $params${\tt .} $proof$ ~~$|$~~
|
berghofe@11622
|
946 |
$\Lambda params${\tt .} $proof$ \\
|
berghofe@11622
|
947 |
& $|$ & $proof$ \verb!%! $any$ ~~$|$~~
|
berghofe@11622
|
948 |
$proof$ $\cdot$ $any$ \\
|
berghofe@11622
|
949 |
& $|$ & $proof$ \verb!%%! $proof$ ~~$|$~~
|
berghofe@11622
|
950 |
$proof$ {\boldmath$\cdot$} $proof$ \\
|
berghofe@11622
|
951 |
& $|$ & $id$ ~~$|$~~ $longid$ \\\\
|
berghofe@11622
|
952 |
$param$ & $=$ & $idt$ ~~$|$~~ $idt$ {\tt :} $prop$ ~~$|$~~
|
berghofe@11622
|
953 |
{\tt (} $param$ {\tt )} \\\\
|
berghofe@11622
|
954 |
$params$ & $=$ & $param$ ~~$|$~~ $param$ $params$
|
berghofe@11622
|
955 |
\end{tabular}
|
berghofe@11622
|
956 |
\end{center}
|
berghofe@11622
|
957 |
\caption{Proof term syntax}\label{fig:proof_gram}
|
berghofe@11622
|
958 |
\end{figure}
|
berghofe@11622
|
959 |
The function {\tt read_proof} reads in a proof term with
|
berghofe@11622
|
960 |
respect to a given theory. The boolean flag indicates whether
|
berghofe@11622
|
961 |
the proof term to be parsed contains explicit typing information
|
berghofe@11622
|
962 |
to be taken into account.
|
berghofe@11622
|
963 |
Usually, typing information is left implicit and
|
berghofe@11622
|
964 |
is inferred during proof reconstruction. The pretty printing
|
berghofe@11622
|
965 |
functions operating on theorems take a boolean flag as an
|
berghofe@11622
|
966 |
argument which indicates whether the proof term should
|
berghofe@11622
|
967 |
be reconstructed before printing.
|
berghofe@11622
|
968 |
|
berghofe@11622
|
969 |
The following example (based on Isabelle/HOL) illustrates how
|
berghofe@11622
|
970 |
to parse and check proof terms. We start by parsing a partial
|
berghofe@11622
|
971 |
proof term
|
berghofe@11622
|
972 |
\begin{ttbox}
|
berghofe@11622
|
973 |
val prf = ProofSyntax.read_proof Main.thy false
|
berghofe@11622
|
974 |
"impI % _ % _ %% (Lam H : _. conjE % _ % _ % _ %% H %%
|
berghofe@11622
|
975 |
(Lam (H1 : _) H2 : _. conjI % _ % _ %% H2 %% H1))";
|
berghofe@11622
|
976 |
{\out val prf = PThm (("HOL.impI", []), \dots, \dots, None) % None % None %%}
|
berghofe@11622
|
977 |
{\out AbsP ("H", None, PThm (("HOL.conjE", []), \dots, \dots, None) %}
|
berghofe@11622
|
978 |
{\out None % None % None %% PBound 0 %%}
|
berghofe@11622
|
979 |
{\out AbsP ("H1", None, AbsP ("H2", None, \dots))) : Proofterm.proof}
|
berghofe@11622
|
980 |
\end{ttbox}
|
berghofe@11622
|
981 |
The statement to be established by this proof is
|
berghofe@11622
|
982 |
\begin{ttbox}
|
berghofe@11622
|
983 |
val t = term_of
|
berghofe@11622
|
984 |
(read_cterm (sign_of Main.thy) ("A & B --> B & A", propT));
|
berghofe@11622
|
985 |
{\out val t = Const ("Trueprop", "bool => prop") $}
|
berghofe@11622
|
986 |
{\out (Const ("op -->", "[bool, bool] => bool") $}
|
berghofe@11622
|
987 |
{\out \dots $ \dots : Term.term}
|
berghofe@11622
|
988 |
\end{ttbox}
|
berghofe@11622
|
989 |
Using {\tt t} we can reconstruct the full proof
|
berghofe@11622
|
990 |
\begin{ttbox}
|
berghofe@11622
|
991 |
val prf' = Reconstruct.reconstruct_proof (sign_of Main.thy) t prf;
|
berghofe@11622
|
992 |
{\out val prf' = PThm (("HOL.impI", []), \dots, \dots, Some []) %}
|
berghofe@11622
|
993 |
{\out Some (Const ("op &", \dots) $ Free ("A", \dots) $ Free ("B", \dots)) %}
|
berghofe@11622
|
994 |
{\out Some (Const ("op &", \dots) $ Free ("B", \dots) $ Free ("A", \dots)) %%}
|
berghofe@11622
|
995 |
{\out AbsP ("H", Some (Const ("Trueprop", \dots) $ \dots), \dots)}
|
berghofe@11622
|
996 |
{\out : Proofterm.proof}
|
berghofe@11622
|
997 |
\end{ttbox}
|
berghofe@11622
|
998 |
This proof can finally be turned into a theorem
|
berghofe@11622
|
999 |
\begin{ttbox}
|
berghofe@11622
|
1000 |
val thm = ProofChecker.thm_of_proof Main.thy prf';
|
berghofe@11622
|
1001 |
{\out val thm = "A & B --> B & A" : Thm.thm}
|
berghofe@11622
|
1002 |
\end{ttbox}
|
berghofe@11622
|
1003 |
|
berghofe@11622
|
1004 |
\index{proof terms|)}
|
berghofe@11622
|
1005 |
\index{theorems|)}
|
berghofe@7871
|
1006 |
|
wenzelm@5371
|
1007 |
|
wenzelm@5371
|
1008 |
%%% Local Variables:
|
wenzelm@5371
|
1009 |
%%% mode: latex
|
wenzelm@5371
|
1010 |
%%% TeX-master: "ref"
|
wenzelm@5371
|
1011 |
%%% End:
|