\chapter{Syntax primitives}

 The rather generic framework of Isabelle/Isar syntax emerges from three main

 syntactic categories: \emph{commands} of the top-level Isar engine (covering

 theory and proof elements), \emph{methods} for general goal refinements

 (analogous to traditional ``tactics''), and \emph{attributes} for operations

 on facts (within a certain context).  Here we give a reference of basic

 syntactic entities underlying Isabelle/Isar syntax in a bottom-up manner.

 Concrete theory and proof language elements will be introduced later on.

 \medskip

 In order to get started with writing well-formed Isabelle/Isar documents, the

 most important aspect to be noted is the difference of \emph{inner} versus

 \emph{outer} syntax.  Inner syntax is that of Isabelle types and terms of the

 logic, while outer syntax is that of Isabelle/Isar theory sources (including

 proofs).  As a general rule, inner syntax entities may occur only as

 \emph{atomic entities} within outer syntax.  For example, the string

 \texttt{"x + y"} and identifier \texttt{z} are legal term specifications

 within a theory, while \texttt{x + y} is not.

 \begin{warn}

   Old-style Isabelle theories used to fake parts of the inner syntax of types,

   with rather complicated rules when quotes may be omitted.  Despite the minor

   drawback of requiring quotes more often, the syntax of Isabelle/Isar is

   somewhat simpler and more robust in that respect.

 \end{warn}

 Printed theory documents usually omit quotes to gain readability (this is a

 matter of {\LaTeX} macro setup, say via \verb,\isabellestyle,, see also

 \cite{isabelle-sys}).  Experienced users of Isabelle/Isar may easily

 reconstruct the lost technical information, while mere readers need not care

 about quotes at all.

 \medskip

 Isabelle/Isar input may contain any number of input termination characters

 ``\texttt{;}'' (semicolon) to separate commands explicitly.  This is

 particularly useful in interactive shell sessions to make clear where the

 current command is intended to end.  Otherwise, the interpreter loop will

 continue to issue a secondary prompt ``\verb,#,'' until an end-of-command is

 clearly recognized from the input syntax, e.g.\ encounter of the next command

 keyword.

 Advanced interfaces such as Proof~General \cite{proofgeneral} do not require

 explicit semicolons, the amount of input text is determined automatically by

 inspecting the present content of the Emacs text buffer.  In the printed

 presentation of Isabelle/Isar documents semicolons are omitted altogether for

 readability.

 \begin{warn}

   Proof~General requires certain syntax classification tables in order to

   achieve properly synchronized interaction with the Isabelle/Isar process.

   These tables need to be consistent with the Isabelle version and particular

   logic image to be used in a running session (common object-logics may well

   change the outer syntax).  The standard setup should work correctly with any

   of the ``official'' logic images derived from Isabelle/HOL (including HOLCF

   etc.).  Users of alternative logics may need to tell Proof~General

   explicitly, e.g.\ by giving an option \verb,-k ZF, (in conjunction with

   \verb,-l ZF, to specify the default logic image).

 \end{warn}

 \section{Lexical matters}\label{sec:lex-syntax}

 The Isabelle/Isar outer syntax provides token classes as presented below; most

 of these coincide with the inner lexical syntax as presented in

 \cite{isabelle-ref}.

 \indexoutertoken{ident}\indexoutertoken{longident}\indexoutertoken{symident}

 \indexoutertoken{nat}\indexoutertoken{var}\indexoutertoken{typefree}

 \indexoutertoken{typevar}\indexoutertoken{string}\indexoutertoken{altstring}

 \indexoutertoken{verbatim}

 \begin{matharray}{rcl}

   ident & = & letter\,quasiletter^* \\

   longident & = & ident (\verb,.,ident)^+ \\

   symident & = & sym^+ ~|~ \verb,\<,ident\verb,>, \\

   nat & = & digit^+ \\

   var & = & ident ~|~ \verb,?,ident ~|~ \verb,?,ident\verb,.,nat \\

   typefree & = & \verb,',ident \\

   typevar & = & typefree ~|~ \verb,?,typefree ~|~ \verb,?,typefree\verb,.,nat \\

   string & = & \verb,", ~\dots~ \verb,", \\

   altstring & = & \backquote ~\dots~ \backquote \\

   verbatim & = & \verb,{*, ~\dots~ \verb,*}, \\[1ex]

   letter & = & latin ~|~ \verb,\<,latin\verb,>, ~|~ \verb,\<,latin\,latin\verb,>, ~|~ greek ~|~ \\

          &   & \verb,\<^isub>, ~|~ \verb,\<^isup>, \\

   quasiletter & = & letter ~|~ digit ~|~ \verb,_, ~|~ \verb,', \\

   latin & = & \verb,a, ~|~ \dots ~|~ \verb,z, ~|~ \verb,A, ~|~ \dots ~|~ \verb,Z, \\

   digit & = & \verb,0, ~|~ \dots ~|~ \verb,9, \\

   sym & = & \verb,!, ~|~ \verb,#, ~|~ \verb,$, ~|~ \verb,%, ~|~ \verb,&, ~|~  %$

    \verb,*, ~|~ \verb,+, ~|~ \verb,-, ~|~ \verb,/, ~|~ \verb,:, ~|~ \\

   & & \verb,<, ~|~ \verb,=, ~|~ \verb,>, ~|~ \verb,?, ~|~ \texttt{\at} ~|~

   \verb,^, ~|~ \verb,_, ~|~ \verb,|, ~|~ \verb,~, \\

 greek & = & \verb,\<alpha>, ~|~ \verb,\<beta>, ~|~ \verb,\<gamma>, ~|~ \verb,\<delta>, ~| \\

       &   & \verb,\<epsilon>, ~|~ \verb,\<zeta>, ~|~ \verb,\<eta>, ~|~ \verb,\<theta>, ~| \\

       &   & \verb,\<iota>, ~|~ \verb,\<kappa>, ~|~ \verb,\<mu>, ~|~ \verb,\<nu>, ~| \\

       &   & \verb,\<xi>, ~|~ \verb,\<pi>, ~|~ \verb,\<rho>, ~|~ \verb,\<sigma>, ~| \\

       &   & \verb,\<tau>, ~|~ \verb,\<upsilon>, ~|~ \verb,\<phi>, ~|~ \verb,\<psi>, ~| \\

       &   & \verb,\<omega>, ~|~ \verb,\<Gamma>, ~|~ \verb,\<Delta>, ~|~ \verb,\<Theta>, ~| \\

       &   & \verb,\<Lambda>, ~|~ \verb,\<Xi>, ~|~ \verb,\<Pi>, ~|~ \verb,\<Sigma>, ~| \\

       &   & \verb,\<Upsilon>, ~|~ \verb,\<Phi>, ~|~ \verb,\<Psi>, ~|~ \verb,\<Omega>, \\

 \end{matharray}

 The syntax of $string$ admits any characters, including newlines; ``\verb|"|''

 (double-quote) and ``\verb|\|'' (backslash) need to be escaped by a backslash.

 Alternative strings according to $altstring$ are analogous, using single

 back-quotes instead.  The body of $verbatim$ may consist of any text not

 containing ``\verb|*}|''; this allows convenient inclusion of quotes without

 further escapes.  The greek letters do \emph{not} include \verb,\<lambda>,,

 which is already used differently in the meta-logic.

 Common mathematical symbols such as $\forall$ are represented in Isabelle as

 \verb,\<forall>,.  There are infinitely many legal symbols like this, although

 proper presentation is left to front-end tools such as {\LaTeX} or

 Proof~General with the X-Symbol package.  A list of standard Isabelle symbols

 that work well with these tools is given in \cite[appendix~A]{isabelle-sys}.

 Comments take the form \texttt{(*~\dots~*)} and may be nested, although

 user-interface tools may prevent this.  Note that \texttt{(*~\dots~*)}

 indicate source comments only, which are stripped after lexical analysis of

 the input.  The Isar document syntax also provides formal comments that are

 considered as part of the text (see \S\ref{sec:comments}).

 \begin{warn}

   Proof~General does not handle nested comments properly; it is also unable to

   keep \verb,(*,\,/\,\verb,{*, and \verb,*),\,/\,\verb,*}, apart, despite

   their rather different meaning.  These are inherent problems of Emacs

   legacy.  Users should not be overly aggressive about nesting or alternating

   these delimiters.

 \end{warn}

 \section{Common syntax entities}

 Subsequently, we introduce several basic syntactic entities, such as names,

 terms, and theorem specifications, which have been factored out of the actual

 Isar language elements to be described later.

 Note that some of the basic syntactic entities introduced below (e.g.\

 \railqtok{name}) act much like tokens rather than plain nonterminals (e.g.\

 \railnonterm{sort}), especially for the sake of error messages.  E.g.\ syntax

 elements like $\CONSTS$ referring to \railqtok{name} or \railqtok{type} would

 really report a missing name or type rather than any of the constituent

 primitive tokens such as \railtok{ident} or \railtok{string}.

 \subsection{Names}

 Entity \railqtok{name} usually refers to any name of types, constants,

 theorems etc.\ that are to be \emph{declared} or \emph{defined} (so qualified

 identifiers are excluded here).  Quoted strings provide an escape for

 non-identifier names or those ruled out by outer syntax keywords (e.g.\

 \verb|"let"|).  Already existing objects are usually referenced by

 \railqtok{nameref}.

 \indexoutertoken{name}\indexoutertoken{parname}\indexoutertoken{nameref}

 \indexoutertoken{int}

 \begin{rail}

   name: ident | symident | string | nat

   ;

   parname: '(' name ')'

   ;

   nameref: name | longident

   ;

   int: nat | '-' nat

   ;

 \end{rail}

 \subsection{Comments}\label{sec:comments}

 Large chunks of plain \railqtok{text} are usually given \railtok{verbatim},

 i.e.\ enclosed in \verb|{*|~\dots~\verb|*}|.  For convenience, any of the

 smaller text units conforming to \railqtok{nameref} are admitted as well.  A

 marginal \railnonterm{comment} is of the form \texttt{--} \railqtok{text}.

 Any number of these may occur within Isabelle/Isar commands.

 \indexoutertoken{text}\indexouternonterm{comment}

 \begin{rail}

   text: verbatim | nameref

   ;

   comment: '--' text

   ;

 \end{rail}

 \subsection{Type classes, sorts and arities}

 Classes are specified by plain names.  Sorts have a very simple inner syntax,

 which is either a single class name $c$ or a list $\{c@1, \dots, c@n\}$

 referring to the intersection of these classes.  The syntax of type arities is

 given directly at the outer level.

 \railalias{subseteq}{\isasymsubseteq}

 \railterm{subseteq}

 \indexouternonterm{sort}\indexouternonterm{arity}

 \indexouternonterm{classdecl}

 \begin{rail}

   classdecl: name (('<' | subseteq) (nameref + ','))?

   ;

   sort: nameref

   ;

   arity: ('(' (sort + ',') ')')? sort

   ;

 \end{rail}

 \subsection{Types and terms}\label{sec:types-terms}

 The actual inner Isabelle syntax, that of types and terms of the logic, is far

 too sophisticated in order to be modelled explicitly at the outer theory

 level.  Basically, any such entity has to be quoted to turn it into a single

 token (the parsing and type-checking is performed internally later).  For

 convenience, a slightly more liberal convention is adopted: quotes may be

 omitted for any type or term that is already atomic at the outer level.  For

 example, one may just write \texttt{x} instead of \texttt{"x"}.  Note that

 symbolic identifiers (e.g.\ \texttt{++} or $\forall$) are available as well,

 provided these have not been superseded by commands or other keywords already

 (e.g.\ \texttt{=} or \texttt{+}).

 \indexoutertoken{type}\indexoutertoken{term}\indexoutertoken{prop}

 \begin{rail}

   type: nameref | typefree | typevar

   ;

   term: nameref | var

   ;

   prop: term

   ;

 \end{rail}

 Positional instantiations are indicated by giving a sequence of terms, or the

 placeholder ``$\_$'' (underscore), which means to skip a position.

 \indexoutertoken{inst}\indexoutertoken{insts}

 \begin{rail}

   inst: underscore | term

   ;

   insts: (inst *)

   ;

 \end{rail}

 Type declarations and definitions usually refer to \railnonterm{typespec} on

 the left-hand side.  This models basic type constructor application at the

 outer syntax level.  Note that only plain postfix notation is available here,

 but no infixes.

 \indexouternonterm{typespec}

 \begin{rail}

   typespec: (() | typefree | '(' ( typefree + ',' ) ')') name

   ;

 \end{rail}

 \subsection{Mixfix annotations}

 Mixfix annotations specify concrete \emph{inner} syntax of Isabelle types and

 terms.  Some commands such as $\TYPES$ (see \S\ref{sec:types-pure}) admit

 infixes only, while $\CONSTS$ (see \S\ref{sec:consts}) and

 $\isarkeyword{syntax}$ (see \S\ref{sec:syn-trans}) support the full range of

 general mixfixes and binders.

 \indexouternonterm{infix}\indexouternonterm{mixfix}\indexouternonterm{structmixfix}

 \begin{rail}

   infix: '(' ('infix' | 'infixl' | 'infixr') string? nat ')'

   ;

   mixfix: infix | '(' string prios? nat? ')' | '(' 'binder' string prios? nat ')'

   ;

   structmixfix: mixfix | '(' 'structure' ')'

   ;

   prios: '[' (nat + ',') ']'

   ;

 \end{rail}

 Here the \railtok{string} specifications refer to the actual mixfix template

 (see also \cite{isabelle-ref}), which may include literal text, spacing,

 blocks, and arguments (denoted by ``$_$''); the special symbol \verb,\<index>,

 (printed as ``\i'') represents an index argument that specifies an implicit

 structure reference (see also \S\ref{sec:locale}).  Infix and binder

 declarations provide common abbreviations for particular mixfix declarations.

 So in practice, mixfix templates mostly degenerate to literal text for

 concrete syntax, such as ``\verb,++,'' for an infix symbol, or ``\verb,++,\i''

 for an infix of an implicit structure.

 \subsection{Proof methods}\label{sec:syn-meth}

 Proof methods are either basic ones, or expressions composed of methods via

 ``\texttt{,}'' (sequential composition), ``\texttt{|}'' (alternative choices),

 ``\texttt{?}'' (try), ``\texttt{+}'' (repeat at least once).  In practice,

 proof methods are usually just a comma separated list of

 \railqtok{nameref}~\railnonterm{args} specifications.  Note that parentheses

 may be dropped for single method specifications (with no arguments).

 \indexouternonterm{method}

 \begin{rail}

   method: (nameref | '(' methods ')') (() | '?' | '+')

   ;

   methods: (nameref args | method) + (',' | '|')

   ;

 \end{rail}

 Proper use of Isar proof methods does \emph{not} involve goal addressing.

 Nevertheless, specifying goal ranges may occasionally come in handy in

 emulating tactic scripts.  Note that $[n-]$ refers to all goals, starting from

 $n$.  All goals may be specified by $[!]$, which is the same as $[1-]$.

 \indexouternonterm{goalspec}

 \begin{rail}

   goalspec: '[' (nat '-' nat | nat '-' | nat | '!' ) ']'

   ;

 \end{rail}

 \subsection{Attributes and theorems}\label{sec:syn-att}

 Attributes (and proof methods, see \S\ref{sec:syn-meth}) have their own

 ``semi-inner'' syntax, in the sense that input conforming to

 \railnonterm{args} below is parsed by the attribute a second time.  The

 attribute argument specifications may be any sequence of atomic entities

 (identifiers, strings etc.), or properly bracketed argument lists.  Below

 \railqtok{atom} refers to any atomic entity, including any \railtok{keyword}

 conforming to \railtok{symident}.

 \indexoutertoken{atom}\indexouternonterm{args}\indexouternonterm{attributes}

 \begin{rail}

   atom: nameref | typefree | typevar | var | nat | keyword

   ;

   arg: atom | '(' args ')' | '[' args ']'

   ;

   args: arg *

   ;

   attributes: '[' (nameref args * ',') ']'

   ;

 \end{rail}

 Theorem specifications come in several flavors: \railnonterm{axmdecl} and

 \railnonterm{thmdecl} usually refer to axioms, assumptions or results of goal

 statements, while \railnonterm{thmdef} collects lists of existing theorems.

 Existing theorems are given by \railnonterm{thmref} and \railnonterm{thmrefs},

 the former requires an actual singleton result.  There are three forms of

 theorem references: (1) named facts $a$, (2) selections from named facts $a(i,

 j - k)$, or (3) literal fact propositions using $altstring$ syntax

 $\backquote\phi\backquote$, (see also method $fact$ in

 \S\ref{sec:pure-meth-att}).

 Any kind of theorem specification may include lists of attributes both on the

 left and right hand sides; attributes are applied to any immediately preceding

 fact.  If names are omitted, the theorems are not stored within the theorem

 database of the theory or proof context, but any given attributes are applied

 nonetheless.

 \indexouternonterm{axmdecl}\indexouternonterm{thmdecl}

 \indexouternonterm{thmdef}\indexouternonterm{thmref}

 \indexouternonterm{thmrefs}\indexouternonterm{selection}

 \begin{rail}

   axmdecl: name attributes? ':'

   ;

   thmdecl: thmbind ':'

   ;

   thmdef: thmbind '='

   ;

   thmref: (nameref selection? | altstring) attributes?

   ;

   thmrefs: thmref +

   ;

   thmbind: name attributes | name | attributes

   ;

   selection: '(' ((nat | nat '-' nat?) + ',') ')'

   ;

 \end{rail}

 \subsection{Term patterns and declarations}\label{sec:term-decls}

 Wherever explicit propositions (or term fragments) occur in a proof text,

 casual binding of schematic term variables may be given specified via patterns

 of the form ``$\ISS{p@1\;\dots}{p@n}$''.  There are separate versions

 available for \railqtok{term}s and \railqtok{prop}s.  The latter provides a

 $\CONCLNAME$ part with patterns referring the (atomic) conclusion of a rule.

 \indexouternonterm{termpat}\indexouternonterm{proppat}

 \begin{rail}

   termpat: '(' ('is' term +) ')'

   ;

   proppat: '(' (('is' prop +) | 'concl' ('is' prop +) | ('is' prop +) 'concl' ('is' prop +)) ')'

   ;

 \end{rail}

 Declarations of local variables $x :: \tau$ and logical propositions $a :

 \phi$ represent different views on the same principle of introducing a local

 scope.  In practice, one may usually omit the typing of $vars$ (due to

 type-inference), and the naming of propositions (due to implicit references of

 current facts).  In any case, Isar proof elements usually admit to introduce

 multiple such items simultaneously.

 \indexouternonterm{vars}\indexouternonterm{props}

 \begin{rail}

   vars: (name+) ('::' type)?

   ;

   props: thmdecl? (prop proppat? +)

   ;

 \end{rail}

 The treatment of multiple declarations corresponds to the complementary focus

 of $vars$ versus $props$: in ``$x@1~\dots~x@n :: \tau$'' the typing refers to

 all variables, while in $a\colon \phi@1~\dots~\phi@n$ the naming refers to all

 propositions collectively.  Isar language elements that refer to $vars$ or

 $props$ typically admit separate typings or namings via another level of

 iteration, with explicit $\AND$ separators; e.g.\ see $\FIXNAME$ and

 $\ASSUMENAME$ in \S\ref{sec:proof-context}.

 \subsection{Antiquotations}\label{sec:antiq}

 \begin{matharray}{rcl}

   thm & : & \isarantiq \\

   prop & : & \isarantiq \\

   term & : & \isarantiq \\

   const & : & \isarantiq \\

   typeof & : & \isarantiq \\

   typ & : & \isarantiq \\

   thm_style & : & \isarantiq \\

   term_style & : & \isarantiq \\

   text & : & \isarantiq \\

   goals & : & \isarantiq \\

   subgoals & : & \isarantiq \\

   prf & : & \isarantiq \\

   full_prf & : & \isarantiq \\

   ML & : & \isarantiq \\

   ML_type & : & \isarantiq \\

   ML_struct & : & \isarantiq \\

 \end{matharray}

 The text body of formal comments (see also \S\ref{sec:comments}) may contain

 antiquotations of logical entities, such as theorems, terms and types, which

 are to be presented in the final output produced by the Isabelle document

 preparation system (see also \S\ref{sec:document-prep}).

 Thus embedding of

 ``\texttt{{\at}{\ttlbrace}term~[show_types]~"f(x)~=~a~+~x"{\ttrbrace}}''

 within a text block would cause

 \isa{(f{\isasymColon}'a~{\isasymRightarrow}~'a)~(x{\isasymColon}'a)~=~(a{\isasymColon}'a)~+~x}

 to appear in the final {\LaTeX} document.  Also note that theorem

 antiquotations may involve attributes as well.  For example,

 \texttt{{\at}{\ttlbrace}thm~sym~[no_vars]{\ttrbrace}} would print the

 statement where all schematic variables have been replaced by fixed ones,

 which are easier to read.

 \indexisarant{thm}\indexisarant{prop}\indexisarant{term}\indexisarant{const}

 \indexisarant{typeof}\indexisarant{typ}\indexisarant{thm-style}

 \indexisarant{term-style}\indexisarant{text}\indexisarant{goals}

 \indexisarant{subgoals}\indexisarant{prf}\indexisarant{full-prf}\indexisarant{ML}

 \indexisarant{ML-type}\indexisarant{ML-struct}

 \begin{rail}

   atsign lbrace antiquotation rbrace

   ;

   antiquotation:

     'thm' options thmrefs |

     'prop' options prop |

     'term' options term |

     'const' options term |

     'typeof' options term |

     'typ' options type |

     'thm\_style' options name thmref |

     'term\_style' options name term |

     'text' options name |

     'goals' options |

     'subgoals' options |

     'prf' options thmrefs |

     'full\_prf' options thmrefs |

     'ML' options name |

     'ML\_type' options name |

     'ML\_struct' options name

   ;

   options: '[' (option * ',') ']'

   ;

   option: name | name '=' name

   ;

 \end{rail}

 Note that the syntax of antiquotations may \emph{not} include source comments

 \texttt{(*~\dots~*)} or verbatim text \verb|{*|~\dots~\verb|*}|.

 \begin{descr}

 \item [$\at\{thm~\vec a\}$] prints theorems $\vec a$. Note that attribute

   specifications may be included as well (see also \S\ref{sec:syn-att}); the

   $no_vars$ operation (see \S\ref{sec:misc-meth-att}) would be particularly

   useful to suppress printing of schematic variables.

 \item [$\at\{prop~\phi\}$] prints a well-typed proposition $\phi$.

 \item [$\at\{term~t\}$] prints a well-typed term $t$.

 \item [$\at\{const~c\}$] prints a well-defined constant $c$.

 \item [$\at\{typeof~t\}$] prints the type of a well-typed term $t$.

 \item [$\at\{typ~\tau\}$] prints a well-formed type $\tau$.

 \item [$\at\{thm_style~s~a\}$] prints theorem $a$, previously applying a style

   $s$ to it (see below).

 \item [$\at\{term_style~s~t\}$] prints a well-typed term $t$ after applying a

   style $s$ to it (see below).

 \item [$\at\{text~s\}$] prints uninterpreted source text $s$.  This is

   particularly useful to print portions of text according to the Isabelle

   {\LaTeX} output style, without demanding well-formedness (e.g.\ small pieces

   of terms that should not be parsed or type-checked yet).

 \item [$\at\{goals\}$] prints the current \emph{dynamic} goal state.  This is

   mainly for support of tactic-emulation scripts within Isar --- presentation

   of goal states does not conform to actual human-readable proof documents.

   Please do not include goal states into document output unless you really

   know what you are doing!

 \item [$\at\{subgoals\}$] is similar to $goals$, but does not print the main

   goal.

 \item [$\at\{prf~\vec a\}$] prints the (compact) proof terms corresponding to

   the theorems $\vec a$. Note that this requires proof terms to be switched on

   for the current object logic (see the ``Proof terms'' section of the

   Isabelle reference manual for information on how to do this).

 \item [$\at\{full_prf~\vec a\}$] is like $\at\{prf~\vec a\}$, but displays the

   full proof terms, i.e.\ also displays information omitted in the compact

   proof term, which is denoted by ``$_$'' placeholders there.

 \item [$\at\{ML~s\}$, $\at\{ML_type~s\}$, and $\at\{ML_struct~s\}$] check text

   $s$ as ML value, type, and structure, respectively.  If successful, the

   source is displayed verbatim.

 \end{descr}

 \medskip

 The following standard styles for use with $thm_style$ and $term_style$ are

 available:

 \begin{descr}

 \item [$lhs$] extracts the first argument of any application form with at

   least two arguments -- typically meta-level or object-level equality, or any

   other binary relation.

 \item [$rhs$] is like $lhs$, but extracts the second argument.

 \item [$concl$] extracts the conclusion $C$ from a nested meta-level

   implication $A@1 \Imp \cdots A@n \Imp C$.

 \item [$prem1$, \dots, $prem9$] extract premise number $1$, \dots, $9$,

   respectively, from a nested meta-level implication $A@1 \Imp \cdots A@n \Imp

   C$.

 \end{descr}

 \medskip

 The following options are available to tune the output.  Note that most of

 these coincide with ML flags of the same names (see also \cite{isabelle-ref}).

 \begin{descr}

 \item[$show_types = bool$ and $show_sorts = bool$] control printing of

   explicit type and sort constraints.

 \item[$show_structs = bool$] controls printing of implicit structures.

 \item[$long_names = bool$] forces names of types and constants etc.\ to be

   printed in their fully qualified internal form.

 \item[$short_names = bool$] forces names of types and constants etc.\ to be

   printed unqualified.  Note that internalizing the output again in the

   current context may well yield a different result.

 \item[$unique_names = bool$] determines whether the printed version of

   qualified names should be made sufficiently long to avoid overlap with names

   declared further back.  Set to $false$ for more concise output.

 \item[$eta_contract = bool$] prints terms in $\eta$-contracted form.

 \item[$display = bool$] indicates if the text is to be output as multi-line

   ``display material'', rather than a small piece of text without line breaks

   (which is the default).

 \item[$breaks = bool$] controls line breaks in non-display material.

 \item[$quotes = bool$] indicates if the output should be enclosed in double

   quotes.

 \item[$mode = name$] adds $name$ to the print mode to be used for presentation

   (see also \cite{isabelle-ref}).  Note that the standard setup for {\LaTeX}

   output is already present by default, including the modes ``$latex$'',

   ``$xsymbols$'', ``$symbols$''.

 \item[$margin = nat$ and $indent = nat$] change the margin or indentation for

   pretty printing of display material.

 \item[$source = bool$] prints the source text of the antiquotation arguments,

   rather than the actual value.  Note that this does not affect

   well-formedness checks of $thm$, $term$, etc. (only the $text$ antiquotation

   admits arbitrary output).

 \item[$goals_limit = nat$] determines the maximum number of goals to be

   printed.

 \item[$locale = name$] specifies an alternative context used for evaluating

   and printing the subsequent argument.

 \end{descr}

 For boolean flags, ``$name = true$'' may be abbreviated as ``$name$''.  All of

 the above flags are disabled by default, unless changed from ML.

 \medskip Note that antiquotations do not only spare the author from tedious

 typing of logical entities, but also achieve some degree of

 consistency-checking of informal explanations with formal developments:

 well-formedness of terms and types with respect to the current theory or proof

 context is ensured here.

 \subsection{Tagged commands}\label{sec:tags}

 Each Isabelle/Isar command may be decorated by presentation tags:

 \indexouternonterm{tags}

 \begin{rail}

   tags: ( tag * )

   ;

   tag: '\%' (ident | string)

 \end{rail}

 The tags $theory$, $proof$, $ML$ are already pre-declared for certain classes

 of commands:

 \medskip

 \begin{tabular}{ll}

   $theory$ & theory begin and end \\

   $proof$ & all proof commands \\

   $ML$ & all commands involving ML code \\

 \end{tabular}

 \medskip The Isabelle document preparation system (see also

 \cite{isabelle-sys}) allows tagged command regions to be presented

 specifically, e.g.\ to fold proof texts, or drop parts of the text completely.

 For example ``$\BYNAME~\%invisible~(auto)$'' would cause that piece of proof

 to be treated as $invisible$ instead of $proof$ (the default), which may be

 either show or hidden depending on the document setup.  In contrast,

 ``$\BYNAME~\%visible~(auto)$'' would force this text to be shown invariably.

 Explicit tag specifications within a proof apply to all subsequent commands of

 the same level of nesting.  For example,

 ``$\PROOFNAME~\%visible~\dots\QEDNAME$'' would force the whole sub-proof to be

 typeset as $visible$ (unless some of its parts are tagged differently).

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