doc-src/IsarRef/logics.tex

tuned;

\chapter{Object-logic specific elements}\label{ch:logics}

\section{General logic setup}\label{sec:object-logic}

\indexisarcmd{judgment}
\indexisarmeth{atomize}\indexisaratt{atomize}
\indexisaratt{rule-format}\indexisaratt{rulify}

\begin{matharray}{rcl}
  \isarcmd{judgment} & : & \isartrans{theory}{theory} \\
  atomize & : & \isarmeth \\
  atomize & : & \isaratt \\
  rule_format & : & \isaratt \\
  rulify & : & \isaratt \\
\end{matharray}

The very starting point for any Isabelle object-logic is a ``truth judgment''
that links object-level statements to the meta-logic (with its minimal
language of $prop$ that covers universal quantification $\Forall$ and
implication $\Imp$).  Common object-logics are sufficiently expressive to
\emph{internalize} rule statements over $\Forall$ and $\Imp$ within their own
language.  This is useful in certain situations where a rule needs to be
viewed as an atomic statement from the meta-level perspective (e.g.\ $\All x x
\in A \Imp P(x)$ versus $\forall x \in A. P(x)$).

From the following language elements, only the $atomize$ method and
$rule_format$ attribute are occasionally required by end-users, the rest is
for those who need to setup their own object-logic.  In the latter case
existing formulations of Isabelle/FOL or Isabelle/HOL may be taken as
realistic examples.

Generic tools may refer to the information provided by object-logic
declarations internally (e.g.\ locales \S\ref{sec:locale}, or the Classical
Reasoner \S\ref{sec:classical}).

\railalias{ruleformat}{rule\_format}
\railterm{ruleformat}

\begin{rail}
  'judgment' constdecl
  ;
  ruleformat ('(' noasm ')')?
  ;
\end{rail}

\begin{descr}
  
\item [$\isarkeyword{judgment}~c::\sigma~~syn$] declares constant $c$ as the
  truth judgment of the current object-logic.  Its type $\sigma$ should
  specify a coercion of the category of object-level propositions to $prop$ of
  the Pure meta-logic; the mixfix annotation $syn$ would typically just link
  the object language (internally of syntactic category $logic$) with that of
  $prop$.  Only one $\isarkeyword{judgment}$ declaration may be given in any
  theory development.
  
\item [$atomize$] (as a method) rewrites any non-atomic premises of a
  sub-goal, using the meta-level equations declared via $atomize$ (as an
  attribute) beforehand.  As a result, heavily nested goals become amenable to
  fundamental operations such as resolution (cf.\ the $rule$ method) and
  proof-by-assumption (cf.\ $assumption$).
  
  A typical collection of $atomize$ rules for a particular object-logic would
  provide an internalization for each of the connectives of $\Forall$, $\Imp$,
  and $\equiv$.  Meta-level conjunction expressed in the manner of minimal
  higher-order logic as $\All{\PROP\,C} (A \Imp B \Imp \PROP\,C) \Imp PROP\,C$
  should be covered as well (this is particularly important for locales, see
  \S\ref{sec:locale}).
  
\item [$rule_format$] rewrites a theorem by the equalities declared as
  $rulify$ rules in the current object-logic.  By default, the result is fully
  normalized, including assumptions and conclusions at any depth.  The
  $no_asm$ option restricts the transformation to the conclusion of a rule.
  
  In common object-logics (HOL, FOL, ZF), the effect of $rule_format$ is to
  replace (bounded) universal quantification ($\forall$) and implication
  ($\imp$) by the corresponding rule statements over $\Forall$ and $\Imp$.

\end{descr}


\section{HOL}

\subsection{Primitive types}\label{sec:typedef}

\indexisarcmdof{HOL}{typedecl}\indexisarcmdof{HOL}{typedef}
\begin{matharray}{rcl}
  \isarcmd{typedecl} & : & \isartrans{theory}{theory} \\
  \isarcmd{typedef} & : & \isartrans{theory}{proof(prove)} \\
\end{matharray}

\begin{rail}
  'typedecl' typespec infix?
  ;
  'typedef' parname? typespec infix? '=' term
  ;
\end{rail}

\begin{descr}
\item [$\isarkeyword{typedecl}~(\vec\alpha)t$] is similar to the original
  $\isarkeyword{typedecl}$ of Isabelle/Pure (see \S\ref{sec:types-pure}), but
  also declares type arity $t :: (term, \dots, term) term$, making $t$ an
  actual HOL type constructor.
\item [$\isarkeyword{typedef}~(\vec\alpha)t = A$] sets up a goal stating
  non-emptiness of the set $A$.  After finishing the proof, the theory will be
  augmented by a Gordon/HOL-style type definition.  See \cite{isabelle-HOL}
  for more information.  Note that user-level theories usually do not directly
  refer to the HOL $\isarkeyword{typedef}$ primitive, but use more advanced
  packages such as $\isarkeyword{record}$ (see \S\ref{sec:hol-record}) and
  $\isarkeyword{datatype}$ (see \S\ref{sec:hol-datatype}).
\end{descr}


\subsection{Low-level tuples}

\indexisarattof{HOL}{split-format}
\begin{matharray}{rcl}
  split_format^* & : & \isaratt \\
\end{matharray}

\railalias{splitformat}{split\_format}
\railterm{splitformat}
\railterm{complete}

\begin{rail}
  splitformat (((name * ) + 'and') | ('(' complete ')'))
  ;
\end{rail}

\begin{descr}
  
\item [$split_format~\vec p@1 \dots \vec p@n$] puts expressions of low-level
  tuple types into canonical form as specified by the arguments given; $\vec
  p@i$ refers to occurrences in premise $i$ of the rule.  The
  $split_format~(complete)$ form causes \emph{all} arguments in function
  applications to be represented canonically according to their tuple type
  structure.
  
  Note that these operations tend to invent funny names for new local
  parameters to be introduced.

\end{descr}


\subsection{Records}\label{sec:hol-record}

FIXME proof tools (simp, cases/induct; no split!?);

FIXME mixfix syntax;

\indexisarcmdof{HOL}{record}
\begin{matharray}{rcl}
  \isarcmd{record} & : & \isartrans{theory}{theory} \\
\end{matharray}

\begin{rail}
  'record' typespec '=' (type '+')? (constdecl +)
  ;
\end{rail}

\begin{descr}
\item [$\isarkeyword{record}~(\vec\alpha)t = \tau + \vec c :: \vec\sigma$]
  defines extensible record type $(\vec\alpha)t$, derived from the optional
  parent record $\tau$ by adding new field components $\vec c :: \vec\sigma$.
  See \cite{isabelle-HOL,NaraschewskiW-TPHOLs98} for more information on
  simply-typed extensible records.
\end{descr}


\subsection{Datatypes}\label{sec:hol-datatype}

\indexisarcmdof{HOL}{datatype}\indexisarcmdof{HOL}{rep-datatype}
\begin{matharray}{rcl}
  \isarcmd{datatype} & : & \isartrans{theory}{theory} \\
  \isarcmd{rep_datatype} & : & \isartrans{theory}{theory} \\
\end{matharray}

\railalias{repdatatype}{rep\_datatype}
\railterm{repdatatype}

\begin{rail}
  'datatype' (dtspec + 'and')
  ;
  repdatatype (name * ) dtrules
  ;

  dtspec: parname? typespec infix? '=' (cons + '|')
  ;
  cons: name (type * ) mixfix?
  ;
  dtrules: 'distinct' thmrefs 'inject' thmrefs 'induction' thmrefs
\end{rail}

\begin{descr}
\item [$\isarkeyword{datatype}$] defines inductive datatypes in HOL.
\item [$\isarkeyword{rep_datatype}$] represents existing types as inductive
  ones, generating the standard infrastructure of derived concepts (primitive
  recursion etc.).
\end{descr}

The induction and exhaustion theorems generated provide case names according
to the constructors involved, while parameters are named after the types (see
also \S\ref{sec:cases-induct}).

See \cite{isabelle-HOL} for more details on datatypes.  Note that the theory
syntax above has been slightly simplified over the old version, usually
requiring more quotes and less parentheses.  Apart from proper proof methods
for case-analysis and induction, there are also emulations of ML tactics
\texttt{case_tac} and \texttt{induct_tac} available, see
\S\ref{sec:induct_tac}.


\subsection{Recursive functions}\label{sec:recursion}

\indexisarcmdof{HOL}{primrec}\indexisarcmdof{HOL}{recdef}\indexisarcmdof{HOL}{recdef-tc}
\begin{matharray}{rcl}
  \isarcmd{primrec} & : & \isartrans{theory}{theory} \\
  \isarcmd{recdef} & : & \isartrans{theory}{theory} \\
  \isarcmd{recdef_tc}^* & : & \isartrans{theory}{proof(prove)} \\
%FIXME
%  \isarcmd{defer_recdef} & : & \isartrans{theory}{theory} \\
\end{matharray}

\railalias{recdefsimp}{recdef\_simp}
\railterm{recdefsimp}

\railalias{recdefcong}{recdef\_cong}
\railterm{recdefcong}

\railalias{recdefwf}{recdef\_wf}
\railterm{recdefwf}

\railalias{recdeftc}{recdef\_tc}
\railterm{recdeftc}

\begin{rail}
  'primrec' parname? (equation + )
  ;
  'recdef' ('(' 'permissive' ')')? \\ name term (prop + ) hints?
  ;
  recdeftc thmdecl? tc
  ;

  equation: thmdecl? prop
  ;
  hints: '(' 'hints' (recdefmod * ) ')'
  ;
  recdefmod: ((recdefsimp | recdefcong | recdefwf) (() | 'add' | 'del') ':' thmrefs) | clasimpmod
  ;
  tc: nameref ('(' nat ')')?
  ;
\end{rail}

\begin{descr}
\item [$\isarkeyword{primrec}$] defines primitive recursive functions over
  datatypes, see also \cite{isabelle-HOL}.
\item [$\isarkeyword{recdef}$] defines general well-founded recursive
  functions (using the TFL package), see also \cite{isabelle-HOL}.  The
  $(permissive)$ option tells TFL to recover from failed proof attempts,
  returning unfinished results.  The $recdef_simp$, $recdef_cong$, and
  $recdef_wf$ hints refer to auxiliary rules to be used in the internal
  automated proof process of TFL.  Additional $clasimpmod$ declarations (cf.\ 
  \S\ref{sec:clasimp}) may be given to tune the context of the Simplifier
  (cf.\ \S\ref{sec:simplifier}) and Classical reasoner (cf.\ 
  \S\ref{sec:classical}).
\item [$\isarkeyword{recdef_tc}~c~(i)$] recommences the proof for leftover
  termination condition number $i$ (default $1$) as generated by a
  $\isarkeyword{recdef}$ definition of constant $c$.
  
  Note that in most cases, $\isarkeyword{recdef}$ is able to finish its
  internal proofs without manual intervention.
\end{descr}

Both kinds of recursive definitions accommodate reasoning by induction (cf.\ 
\S\ref{sec:cases-induct}): rule $c\mathord{.}induct$ (where $c$ is the name of
the function definition) refers to a specific induction rule, with parameters
named according to the user-specified equations.  Case names of
$\isarkeyword{primrec}$ are that of the datatypes involved, while those of
$\isarkeyword{recdef}$ are numbered (starting from $1$).

The equations provided by these packages may be referred later as theorem list
$f\mathord.simps$, where $f$ is the (collective) name of the functions
defined.  Individual equations may be named explicitly as well; note that for
$\isarkeyword{recdef}$ each specification given by the user may result in
several theorems.

\medskip Hints for $\isarkeyword{recdef}$ may be also declared globally, using
the following attributes.

\indexisarattof{HOL}{recdef-simp}\indexisarattof{HOL}{recdef-cong}\indexisarattof{HOL}{recdef-wf}
\begin{matharray}{rcl}
  recdef_simp & : & \isaratt \\
  recdef_cong & : & \isaratt \\
  recdef_wf & : & \isaratt \\
\end{matharray}

\railalias{recdefsimp}{recdef\_simp}
\railterm{recdefsimp}

\railalias{recdefcong}{recdef\_cong}
\railterm{recdefcong}

\railalias{recdefwf}{recdef\_wf}
\railterm{recdefwf}

\begin{rail}
  (recdefsimp | recdefcong | recdefwf) (() | 'add' | 'del')
  ;
\end{rail}


\subsection{(Co)Inductive sets}\label{sec:hol-inductive}

\indexisarcmdof{HOL}{inductive}\indexisarcmdof{HOL}{coinductive}\indexisarattof{HOL}{mono}
\begin{matharray}{rcl}
  \isarcmd{inductive} & : & \isartrans{theory}{theory} \\
  \isarcmd{coinductive} & : & \isartrans{theory}{theory} \\
  mono & : & \isaratt \\
\end{matharray}

\railalias{condefs}{con\_defs}
\railterm{condefs}

\begin{rail}
  ('inductive' | 'coinductive') sets intros monos?
  ;
  'mono' (() | 'add' | 'del')
  ;

  sets: (term +)
  ;
  intros: 'intros' (thmdecl? prop +)
  ;
  monos: 'monos' thmrefs
  ;
\end{rail}

\begin{descr}
\item [$\isarkeyword{inductive}$ and $\isarkeyword{coinductive}$] define
  (co)inductive sets from the given introduction rules.
\item [$mono$] declares monotonicity rules.  These rule are involved in the
  automated monotonicity proof of $\isarkeyword{inductive}$.
\end{descr}

See \cite{isabelle-HOL} for further information on inductive definitions in
HOL.


\subsection{Arithmetic proof support}

\indexisarmethof{HOL}{arith}\indexisarattof{HOL}{arith-split}
\begin{matharray}{rcl}
  arith & : & \isarmeth \\
  arith_split & : & \isaratt \\
\end{matharray}

\begin{rail}
  'arith' '!'?
  ;
\end{rail}

The $arith$ method decides linear arithmetic problems (on types $nat$, $int$,
$real$).  Any current facts are inserted into the goal before running the
procedure.  The ``!''~argument causes the full context of assumptions to be
included.  The $arith_split$ attribute declares case split rules to be
expanded before the arithmetic procedure is invoked.

Note that a simpler (but faster) version of arithmetic reasoning is already
performed by the Simplifier.


\subsection{Cases and induction: emulating tactic scripts}\label{sec:induct_tac}

The following important tactical tools of Isabelle/HOL have been ported to
Isar.  These should be never used in proper proof texts!

\indexisarmethof{HOL}{case-tac}\indexisarmethof{HOL}{induct-tac}
\indexisarmethof{HOL}{ind-cases}\indexisarcmdof{HOL}{inductive-cases}
\begin{matharray}{rcl}
  case_tac^* & : & \isarmeth \\
  induct_tac^* & : & \isarmeth \\
  ind_cases^* & : & \isarmeth \\
  \isarcmd{inductive_cases} & : & \isartrans{theory}{theory} \\
\end{matharray}

\railalias{casetac}{case\_tac}
\railterm{casetac}

\railalias{inducttac}{induct\_tac}
\railterm{inducttac}

\railalias{indcases}{ind\_cases}
\railterm{indcases}

\railalias{inductivecases}{inductive\_cases}
\railterm{inductivecases}

\begin{rail}
  casetac goalspec? term rule?
  ;
  inducttac goalspec? (insts * 'and') rule?
  ;
  indcases (prop +)
  ;
  inductivecases thmdecl? (prop +)
  ;

  rule: ('rule' ':' thmref)
  ;
\end{rail}

\begin{descr}
\item [$case_tac$ and $induct_tac$] admit to reason about inductive datatypes
  only (unless an alternative rule is given explicitly).  Furthermore,
  $case_tac$ does a classical case split on booleans; $induct_tac$ allows only
  variables to be given as instantiation.  These tactic emulations feature
  both goal addressing and dynamic instantiation.  Note that named rule cases
  are \emph{not} provided as would be by the proper $induct$ and $cases$ proof
  methods (see \S\ref{sec:cases-induct}).
  
\item [$ind_cases$ and $\isarkeyword{inductive_cases}$] provide an interface
  to the \texttt{mk_cases} operation.  Rules are simplified in an unrestricted
  forward manner.
  
  While $ind_cases$ is a proof method to apply the result immediately as
  elimination rules, $\isarkeyword{inductive_cases}$ provides case split
  theorems at the theory level for later use,
\end{descr}


\section{HOLCF}

\subsection{Mixfix syntax for continuous operations}

\indexisarcmdof{HOLCF}{consts}\indexisarcmdof{HOLCF}{constdefs}

\begin{matharray}{rcl}
  \isarcmd{consts} & : & \isartrans{theory}{theory} \\
  \isarcmd{constdefs} & : & \isartrans{theory}{theory} \\
\end{matharray}

HOLCF provides a separate type for continuous functions $\alpha \rightarrow
\beta$, with an explicit application operator $f \cdot x$.  Isabelle mixfix
syntax normally refers directly to the pure meta-level function type $\alpha
\To \beta$, with application $f\,x$.

The HOLCF variants of $\CONSTS$ and $\CONSTDEFS$ have the same outer syntax as
the pure versions (cf.\ \S\ref{sec:consts}).  Internally, declarations
involving continuous function types are treated specifically, transforming the
syntax template accordingly and generating syntax translation rules for the
abstract and concrete representation of application.

The behavior for plain meta-level function types is unchanged.  Mixed
continuous and meta-level application is \emph{not} supported.

\subsection{Recursive domains}

\indexisarcmdof{HOLCF}{domain}
\begin{matharray}{rcl}
  \isarcmd{domain} & : & \isartrans{theory}{theory} \\
\end{matharray}

\begin{rail}
  'domain' parname? (dmspec + 'and')
  ;

  dmspec: typespec '=' (cons + '|')
  ;
  cons: name (type * ) mixfix?
  ;
  dtrules: 'distinct' thmrefs 'inject' thmrefs 'induction' thmrefs
\end{rail}

Recursive domains in HOLCF are analogous to datatypes in classical HOL (cf.\ 
\S\ref{sec:hol-datatype}).  Mutual recursive is supported, but no nesting nor
arbitrary branching.  Domain constructors may be strict (default) or lazy, the
latter admits to introduce infinitary objects in the typical LCF manner (lazy
lists etc.).

See also \cite{MuellerNvOS99} for further information HOLCF domains in
general.


\section{ZF}

\subsection{Type checking}

FIXME

\subsection{Inductive sets and datatypes}

FIXME


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