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%% $Id$
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\chapter{Theories, Terms and Types} \label{theories}
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\index{theories|(}\index{signatures|bold}
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\index{reading!axioms|see{{\tt assume_ax}}} Theories organize the
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syntax, declarations and axioms of a mathematical development. They
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are built, starting from the {\Pure} or {\CPure} theory, by extending
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and merging existing theories. They have the \ML\ type
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\mltydx{theory}. Theory operations signal errors by raising exception
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\xdx{THEORY}, returning a message and a list of theories.
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Signatures, which contain information about sorts, types, constants and
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syntax, have the \ML\ type~\mltydx{Sign.sg}. For identification, each
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signature carries a unique list of \bfindex{stamps}, which are \ML\
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references to strings. The strings serve as human-readable names; the
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references serve as unique identifiers. Each primitive signature has a
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single stamp. When two signatures are merged, their lists of stamps are
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also merged. Every theory carries a unique signature.
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Terms and types are the underlying representation of logical syntax. Their
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\ML\ definitions are irrelevant to naive Isabelle users. Programmers who
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wish to extend Isabelle may need to know such details, say to code a tactic
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that looks for subgoals of a particular form. Terms and types may be
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`certified' to be well-formed with respect to a given signature.
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\section{Defining theories}\label{sec:ref-defining-theories}
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Theories are defined via theory files $name$\texttt{.thy} (there are also
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\ML-level interfaces which are only intended for people building advanced
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theory definition packages). Appendix~\ref{app:TheorySyntax} presents the
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concrete syntax for theory files; here follows an explanation of the
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constituent parts.
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\begin{description}
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\item[{\it theoryDef}] is the full definition. The new theory is called $id$.
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It is the union of the named {\bf parent
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theories}\indexbold{theories!parent}, possibly extended with new
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components. \thydx{Pure} and \thydx{CPure} are the basic theories, which
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contain only the meta-logic. They differ just in their concrete syntax for
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function applications.
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The new theory begins as a merge of its parents.
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\begin{ttbox}
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Attempt to merge different versions of theories: "\(T@1\)", \(\ldots\), "\(T@n\)"
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\end{ttbox}
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This error may especially occur when a theory is redeclared --- say to
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change an inappropriate definition --- and bindings to old versions persist.
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Isabelle ensures that old and new theories of the same name are not involved
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in a proof.
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\item[$classes$]
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is a series of class declarations. Declaring {\tt$id$ < $id@1$ \dots\
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$id@n$} makes $id$ a subclass of the existing classes $id@1\dots
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id@n$. This rules out cyclic class structures. Isabelle automatically
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computes the transitive closure of subclass hierarchies; it is not
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necessary to declare {\tt c < e} in addition to {\tt c < d} and {\tt d <
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e}.
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\item[$default$]
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introduces $sort$ as the new default sort for type variables. This applies
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to unconstrained type variables in an input string but not to type
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variables created internally. If omitted, the default sort is the listwise
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union of the default sorts of the parent theories (i.e.\ their logical
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intersection).
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\item[$sort$] is a finite set of classes. A single class $id$
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abbreviates the sort $\ttlbrace id\ttrbrace$.
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\item[$types$]
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is a series of type declarations. Each declares a new type constructor
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or type synonym. An $n$-place type constructor is specified by
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$(\alpha@1,\dots,\alpha@n)name$, where the type variables serve only to
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indicate the number~$n$.
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A {\bf type synonym}\indexbold{type synonyms} is an abbreviation
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$(\alpha@1,\dots,\alpha@n)name = \tau$, where $name$ and $\tau$ can
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be strings.
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\item[$infix$]
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declares a type or constant to be an infix operator of priority $nat$
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associating to the left ({\tt infixl}) or right ({\tt infixr}). Only
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2-place type constructors can have infix status; an example is {\tt
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('a,'b)~"*"~(infixr~20)}, which may express binary product types.
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\item[$arities$] is a series of type arity declarations. Each assigns
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arities to type constructors. The $name$ must be an existing type
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constructor, which is given the additional arity $arity$.
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\item[$nonterminals$]\index{*nonterminal symbols} declares purely
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syntactic types to be used as nonterminal symbols of the context
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free grammar.
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\item[$consts$] is a series of constant declarations. Each new
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constant $name$ is given the specified type. The optional $mixfix$
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annotations may attach concrete syntax to the constant.
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\item[$syntax$] \index{*syntax section}\index{print mode} is a variant
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of $consts$ which adds just syntax without actually declaring
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logical constants. This gives full control over a theory's context
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free grammar. The optional $mode$ specifies the print mode where the
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mixfix productions should be added. If there is no \texttt{output}
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option given, all productions are also added to the input syntax
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(regardless of the print mode).
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\item[$mixfix$] \index{mixfix declarations}
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annotations can take three forms:
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\begin{itemize}
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\item A mixfix template given as a $string$ of the form
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{\tt"}\dots{\tt\_}\dots{\tt\_}\dots{\tt"} where the $i$-th underscore
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indicates the position where the $i$-th argument should go. The list
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of numbers gives the priority of each argument. The final number gives
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the priority of the whole construct.
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\item A constant $f$ of type $\tau@1\To(\tau@2\To\tau)$ can be given {\bf
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infix} status.
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\item A constant $f$ of type $(\tau@1\To\tau@2)\To\tau$ can be given {\bf
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binder} status. The declaration {\tt binder} $\cal Q$ $p$ causes
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${\cal Q}\,x.F(x)$ to be treated
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like $f(F)$, where $p$ is the priority.
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\end{itemize}
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\item[$trans$]
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specifies syntactic translation rules (macros). There are three forms:
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parse rules ({\tt =>}), print rules ({\tt <=}), and parse/print rules ({\tt
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==}).
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\item[$rules$]
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is a series of rule declarations. Each has a name $id$ and the formula is
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given by the $string$. Rule names must be distinct within any single
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theory.
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\item[$defs$] is a series of definitions. They are just like $rules$, except
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that every $string$ must be a definition (see below for details).
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\item[$constdefs$] combines the declaration of constants and their
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definition. The first $string$ is the type, the second the definition.
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\item[$axclass$] \index{*axclass section} defines an
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\rmindex{axiomatic type class} as the intersection of existing
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classes, with additional axioms holding. Class axioms may not
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contain more than one type variable. The class axioms (with implicit
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sort constraints added) are bound to the given names. Furthermore a
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class introduction rule is generated, which is automatically
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employed by $instance$ to prove instantiations of this class.
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\item[$instance$] \index{*instance section} proves class inclusions or
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type arities at the logical level and then transfers these to the
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type signature. The instantiation is proven and checked properly.
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The user has to supply sufficient witness information: theorems
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($longident$), axioms ($string$), or even arbitrary \ML{} tactic
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code $verbatim$.
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\item[$oracle$] links the theory to a trusted external reasoner. It is
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allowed to create theorems, but each theorem carries a proof object
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describing the oracle invocation. See \S\ref{sec:oracles} for details.
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\item[$local$, $global$] change the current name declaration mode.
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Initially, theories start in $local$ mode, causing all names of
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types, constants, axioms etc.\ to be automatically qualified by the
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theory name. Changing this to $global$ causes all names to be
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declared as short base names only.
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The $local$ and $global$ declarations act like switches, affecting
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all following theory sections until changed again explicitly. Also
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note that the final state at the end of the theory will persist. In
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particular, this determines how the names of theorems stored later
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on are handled.
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\item[$setup$]\index{*setup!theory} applies a list of ML functions to
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the theory. The argument should denote a value of type
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\texttt{(theory -> theory) list}. Typically, ML packages are
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initialized in this way.
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\item[$ml$] \index{*ML section}
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consists of \ML\ code, typically for parse and print translation functions.
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\end{description}
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%
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Chapters~\ref{Defining-Logics} and \ref{chap:syntax} explain mixfix
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declarations, translation rules and the {\tt ML} section in more detail.
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\subsection{Definitions}\indexbold{definitions}
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{\bf Definitions} are intended to express abbreviations. The simplest
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form of a definition is $f \equiv t$, where $f$ is a constant.
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Isabelle also allows a derived forms where the arguments of~$f$ appear
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on the left, abbreviating a string of $\lambda$-abstractions.
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Isabelle makes the following checks on definitions:
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\begin{itemize}
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\item Arguments (on the left-hand side) must be distinct variables.
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\item All variables on the right-hand side must also appear on the left-hand
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side.
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\item All type variables on the right-hand side must also appear on
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the left-hand side; this prohibits definitions such as {\tt
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(zero::nat) == length ([]::'a list)}.
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\item The definition must not be recursive. Most object-logics provide
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definitional principles that can be used to express recursion safely.
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\end{itemize}
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These checks are intended to catch the sort of errors that might be made
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accidentally. Misspellings, for instance, might result in additional
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variables appearing on the right-hand side. More elaborate checks could be
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made, but the cost might be overly strict rules on declaration order, etc.
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\subsection{*Classes and arities}
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\index{classes!context conditions}\index{arities!context conditions}
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In order to guarantee principal types~\cite{nipkow-prehofer},
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arity declarations must obey two conditions:
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\begin{itemize}
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\item There must not be any two declarations $ty :: (\vec{r})c$ and
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$ty :: (\vec{s})c$ with $\vec{r} \neq \vec{s}$. For example, this
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excludes the following:
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\begin{ttbox}
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arities
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foo :: ({\ttlbrace}logic{\ttrbrace}) logic
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foo :: ({\ttlbrace}{\ttrbrace})logic
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\end{ttbox}
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\item If there are two declarations $ty :: (s@1,\dots,s@n)c$ and $ty ::
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(s@1',\dots,s@n')c'$ such that $c' < c$ then $s@i' \preceq s@i$ must hold
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for $i=1,\dots,n$. The relationship $\preceq$, defined as
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\[ s' \preceq s \iff \forall c\in s. \exists c'\in s'.~ c'\le c, \]
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expresses that the set of types represented by $s'$ is a subset of the
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set of types represented by $s$. Assuming $term \preceq logic$, the
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following is forbidden:
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\begin{ttbox}
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arities
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foo :: ({\ttlbrace}logic{\ttrbrace})logic
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foo :: ({\ttlbrace}{\ttrbrace})term
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\end{ttbox}
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\end{itemize}
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\section{The theory loader}\label{sec:more-theories}
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\index{theories!reading}\index{files!reading}
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Isabelle's theory loader manages dependencies of the internal graph of theory
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nodes (the \emph{theory database}) and the external view of the file system.
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See \S\ref{sec:intro-theories} for its most basic commands, such as
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\texttt{use_thy}. There are a few more operations available.
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\begin{ttbox}
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use_thy_only : string -> unit
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update_thy : string -> unit
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touch_thy : string -> unit
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delete_tmpfiles : bool ref \hfill{\bf initially true}
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\end{ttbox}
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\begin{ttdescription}
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\item[\ttindexbold{use_thy_only} "$name$";] is similar to \texttt{use_thy},
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but processes the actual theory file $name$\texttt{.thy} only, ignoring
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$name$\texttt{.ML}. This might be useful in replaying proof scripts by hand
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from the very beginning, starting with the fresh theory.
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\item[\ttindexbold{update_thy} "$name$";] is similar to \texttt{use_thy}, but
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ensures that theory $name$ is fully up-to-date with respect to the file
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system --- apart from $name$ itself any of its ancestors may be reloaded as
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well.
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\item[\ttindexbold{touch_thy} "$name$";] marks theory node $name$ of the
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internal graph as outdated. While the theory remains usable, subsequent
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operations such as \texttt{use_thy} may cause a reload.
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\item[reset \ttindexbold{delete_tmpfiles};] processing theory files usually
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involves temporary {\ML} files to be created. By default, these are deleted
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afterwards. Resetting the \texttt{delete_tmpfiles} flag inhibits this,
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|
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leaving the generated code for debugging purposes. The basic location for
|
wenzelm@6568
|
273 |
temporary files is determined by the \texttt{ISABELLE_TMP} environment
|
wenzelm@6571
|
274 |
variable (which is private to the running Isabelle process and may be
|
wenzelm@6568
|
275 |
retrieved by \ttindex{getenv} from {\ML}).
|
wenzelm@6568
|
276 |
\end{ttdescription}
|
clasohm@138
|
277 |
|
wenzelm@6568
|
278 |
\medskip Theory and {\ML} files are located by skimming through the
|
wenzelm@6568
|
279 |
directories listed in Isabelle's internal load path, which merely contains the
|
wenzelm@6568
|
280 |
current directory ``\texttt{.}'' by default. The load path may be accessed by
|
wenzelm@6568
|
281 |
the following operations.
|
lcp@286
|
282 |
|
wenzelm@864
|
283 |
\begin{ttbox}
|
wenzelm@6568
|
284 |
show_path: unit -> string list
|
wenzelm@6568
|
285 |
add_path: string -> unit
|
wenzelm@6568
|
286 |
del_path: string -> unit
|
wenzelm@6568
|
287 |
reset_path: unit -> unit
|
lcp@286
|
288 |
\end{ttbox}
|
clasohm@138
|
289 |
|
lcp@324
|
290 |
\begin{ttdescription}
|
wenzelm@6568
|
291 |
\item[\ttindexbold{show_path}();] displays the load path components in
|
wenzelm@6571
|
292 |
canonical string representation (which is always according to Unix rules).
|
wenzelm@6568
|
293 |
|
wenzelm@6569
|
294 |
\item[\ttindexbold{add_path} "$dir$";] adds component $dir$ to the beginning
|
wenzelm@6569
|
295 |
of the load path.
|
wenzelm@6568
|
296 |
|
wenzelm@6569
|
297 |
\item[\ttindexbold{del_path} "$dir$";] removes any occurrences of component
|
wenzelm@6568
|
298 |
$dir$ from the load path.
|
wenzelm@6568
|
299 |
|
wenzelm@6568
|
300 |
\item[\ttindexbold{reset_path}();] resets the load path to ``\texttt{.}''
|
wenzelm@6568
|
301 |
(current directory) only.
|
lcp@324
|
302 |
\end{ttdescription}
|
clasohm@138
|
303 |
|
wenzelm@6571
|
304 |
In operations referring indirectly to some file, the argument may be prefixed
|
wenzelm@6571
|
305 |
by a directory that will be used as temporary load path, e.g.\
|
wenzelm@6571
|
306 |
\texttt{use_thy~"$dir/name$"}. Note that, depending on which parts of the
|
wenzelm@6571
|
307 |
ancestry of $name$ are already loaded, the dynamic change of paths might be
|
wenzelm@6571
|
308 |
hard to predict. Use this feature with care only.
|
lcp@104
|
309 |
|
lcp@104
|
310 |
|
clasohm@866
|
311 |
\section{Basic operations on theories}\label{BasicOperationsOnTheories}
|
wenzelm@4384
|
312 |
|
wenzelm@4384
|
313 |
\subsection{*Theory inclusion}
|
wenzelm@4384
|
314 |
\begin{ttbox}
|
wenzelm@4384
|
315 |
subthy : theory * theory -> bool
|
wenzelm@4384
|
316 |
eq_thy : theory * theory -> bool
|
wenzelm@4384
|
317 |
transfer : theory -> thm -> thm
|
wenzelm@4384
|
318 |
transfer_sg : Sign.sg -> thm -> thm
|
wenzelm@4384
|
319 |
\end{ttbox}
|
wenzelm@4384
|
320 |
|
wenzelm@4384
|
321 |
Inclusion and equality of theories is determined by unique
|
wenzelm@4384
|
322 |
identification stamps that are created when declaring new components.
|
wenzelm@4384
|
323 |
Theorems contain a reference to the theory (actually to its signature)
|
wenzelm@4384
|
324 |
they have been derived in. Transferring theorems to super theories
|
wenzelm@4384
|
325 |
has no logical significance, but may affect some operations in subtle
|
wenzelm@4384
|
326 |
ways (e.g.\ implicit merges of signatures when applying rules, or
|
wenzelm@4384
|
327 |
pretty printing of theorems).
|
wenzelm@4384
|
328 |
|
wenzelm@4384
|
329 |
\begin{ttdescription}
|
wenzelm@4384
|
330 |
|
wenzelm@4384
|
331 |
\item[\ttindexbold{subthy} ($thy@1$, $thy@2$)] determines if $thy@1$
|
wenzelm@4384
|
332 |
is included in $thy@2$ wrt.\ identification stamps.
|
wenzelm@4384
|
333 |
|
wenzelm@4384
|
334 |
\item[\ttindexbold{eq_thy} ($thy@1$, $thy@2$)] determines if $thy@1$
|
wenzelm@4384
|
335 |
is exactly the same as $thy@2$.
|
wenzelm@4384
|
336 |
|
wenzelm@4384
|
337 |
\item[\ttindexbold{transfer} $thy$ $thm$] transfers theorem $thm$ to
|
wenzelm@4384
|
338 |
theory $thy$, provided the latter includes the theory of $thm$.
|
wenzelm@4384
|
339 |
|
wenzelm@4384
|
340 |
\item[\ttindexbold{transfer_sg} $sign$ $thm$] is similar to
|
wenzelm@4384
|
341 |
\texttt{transfer}, but identifies the super theory via its
|
wenzelm@4384
|
342 |
signature.
|
wenzelm@4384
|
343 |
|
wenzelm@4384
|
344 |
\end{ttdescription}
|
wenzelm@4384
|
345 |
|
wenzelm@4384
|
346 |
|
wenzelm@6571
|
347 |
\subsection{*Primitive theories}
|
wenzelm@864
|
348 |
\begin{ttbox}
|
wenzelm@4317
|
349 |
ProtoPure.thy : theory
|
wenzelm@3108
|
350 |
Pure.thy : theory
|
wenzelm@3108
|
351 |
CPure.thy : theory
|
lcp@286
|
352 |
\end{ttbox}
|
wenzelm@3108
|
353 |
\begin{description}
|
wenzelm@4317
|
354 |
\item[\ttindexbold{ProtoPure.thy}, \ttindexbold{Pure.thy},
|
wenzelm@4317
|
355 |
\ttindexbold{CPure.thy}] contain the syntax and signature of the
|
wenzelm@4317
|
356 |
meta-logic. There are basically no axioms: meta-level inferences
|
wenzelm@4317
|
357 |
are carried out by \ML\ functions. \texttt{Pure} and \texttt{CPure}
|
wenzelm@4317
|
358 |
just differ in their concrete syntax of prefix function application:
|
wenzelm@4317
|
359 |
$t(u@1, \ldots, u@n)$ in \texttt{Pure} vs.\ $t\,u@1,\ldots\,u@n$ in
|
wenzelm@4317
|
360 |
\texttt{CPure}. \texttt{ProtoPure} is their common parent,
|
wenzelm@4317
|
361 |
containing no syntax for printing prefix applications at all!
|
wenzelm@6571
|
362 |
|
wenzelm@6571
|
363 |
%%FIXME
|
wenzelm@6571
|
364 |
%\item[\ttindexbold{merge_theories} $name$ ($thy@1$, $thy@2$)] merges
|
wenzelm@6571
|
365 |
% the two theories $thy@1$ and $thy@2$, creating a new named theory
|
wenzelm@6571
|
366 |
% node. The resulting theory contains all of the syntax, signature
|
wenzelm@6571
|
367 |
% and axioms of the constituent theories. Merging theories that
|
wenzelm@6571
|
368 |
% contain different identification stamps of the same name fails with
|
wenzelm@6571
|
369 |
% the following message
|
wenzelm@864
|
370 |
|
wenzelm@864
|
371 |
%% FIXME
|
nipkow@478
|
372 |
%\item [\ttindexbold{extend_theory} $thy$ {\tt"}$T${\tt"} $\cdots$] extends
|
nipkow@478
|
373 |
% the theory $thy$ with new types, constants, etc. $T$ identifies the theory
|
nipkow@478
|
374 |
% internally. When a theory is redeclared, say to change an incorrect axiom,
|
nipkow@478
|
375 |
% bindings to the old axiom may persist. Isabelle ensures that the old and
|
nipkow@478
|
376 |
% new theories are not involved in the same proof. Attempting to combine
|
nipkow@478
|
377 |
% different theories having the same name $T$ yields the fatal error
|
nipkow@478
|
378 |
%extend_theory : theory -> string -> \(\cdots\) -> theory
|
wenzelm@864
|
379 |
%\begin{ttbox}
|
wenzelm@864
|
380 |
%Attempt to merge different versions of theory: \(T\)
|
wenzelm@864
|
381 |
%\end{ttbox}
|
wenzelm@3108
|
382 |
\end{description}
|
lcp@286
|
383 |
|
wenzelm@864
|
384 |
%% FIXME
|
nipkow@275
|
385 |
%\item [\ttindexbold{extend_theory} $thy$ {\tt"}$T${\tt"}
|
nipkow@275
|
386 |
% ($classes$, $default$, $types$, $arities$, $consts$, $sextopt$) $rules$]
|
nipkow@275
|
387 |
%\hfill\break %%% include if line is just too short
|
lcp@286
|
388 |
%is the \ML{} equivalent of the following theory definition:
|
nipkow@275
|
389 |
%\begin{ttbox}
|
nipkow@275
|
390 |
%\(T\) = \(thy\) +
|
nipkow@275
|
391 |
%classes \(c\) < \(c@1\),\(\dots\),\(c@m\)
|
nipkow@275
|
392 |
% \dots
|
nipkow@275
|
393 |
%default {\(d@1,\dots,d@r\)}
|
nipkow@275
|
394 |
%types \(tycon@1\),\dots,\(tycon@i\) \(n\)
|
nipkow@275
|
395 |
% \dots
|
nipkow@275
|
396 |
%arities \(tycon@1'\),\dots,\(tycon@j'\) :: (\(s@1\),\dots,\(s@n\))\(c\)
|
nipkow@275
|
397 |
% \dots
|
nipkow@275
|
398 |
%consts \(b@1\),\dots,\(b@k\) :: \(\tau\)
|
nipkow@275
|
399 |
% \dots
|
nipkow@275
|
400 |
%rules \(name\) \(rule\)
|
nipkow@275
|
401 |
% \dots
|
nipkow@275
|
402 |
%end
|
nipkow@275
|
403 |
%\end{ttbox}
|
nipkow@275
|
404 |
%where
|
nipkow@275
|
405 |
%\begin{tabular}[t]{l@{~=~}l}
|
nipkow@275
|
406 |
%$classes$ & \tt[("$c$",["$c@1$",\dots,"$c@m$"]),\dots] \\
|
nipkow@275
|
407 |
%$default$ & \tt["$d@1$",\dots,"$d@r$"]\\
|
nipkow@275
|
408 |
%$types$ & \tt[([$tycon@1$,\dots,$tycon@i$], $n$),\dots] \\
|
nipkow@275
|
409 |
%$arities$ & \tt[([$tycon'@1$,\dots,$tycon'@j$], ([$s@1$,\dots,$s@n$],$c$)),\dots]
|
nipkow@275
|
410 |
%\\
|
nipkow@275
|
411 |
%$consts$ & \tt[([$b@1$,\dots,$b@k$],$\tau$),\dots] \\
|
nipkow@275
|
412 |
%$rules$ & \tt[("$name$",$rule$),\dots]
|
nipkow@275
|
413 |
%\end{tabular}
|
lcp@104
|
414 |
|
lcp@104
|
415 |
|
wenzelm@864
|
416 |
\subsection{Inspecting a theory}\label{sec:inspct-thy}
|
lcp@104
|
417 |
\index{theories!inspecting|bold}
|
wenzelm@864
|
418 |
\begin{ttbox}
|
wenzelm@4317
|
419 |
print_syntax : theory -> unit
|
wenzelm@4317
|
420 |
print_theory : theory -> unit
|
wenzelm@4317
|
421 |
parents_of : theory -> theory list
|
wenzelm@4317
|
422 |
ancestors_of : theory -> theory list
|
wenzelm@4317
|
423 |
sign_of : theory -> Sign.sg
|
wenzelm@4317
|
424 |
Sign.stamp_names_of : Sign.sg -> string list
|
lcp@104
|
425 |
\end{ttbox}
|
wenzelm@864
|
426 |
These provide means of viewing a theory's components.
|
lcp@324
|
427 |
\begin{ttdescription}
|
wenzelm@3108
|
428 |
\item[\ttindexbold{print_syntax} $thy$] prints the syntax of $thy$
|
wenzelm@3108
|
429 |
(grammar, macros, translation functions etc., see
|
wenzelm@3108
|
430 |
page~\pageref{pg:print_syn} for more details).
|
wenzelm@3108
|
431 |
|
wenzelm@3108
|
432 |
\item[\ttindexbold{print_theory} $thy$] prints the logical parts of
|
wenzelm@3108
|
433 |
$thy$, excluding the syntax.
|
wenzelm@4317
|
434 |
|
wenzelm@4317
|
435 |
\item[\ttindexbold{parents_of} $thy$] returns the direct ancestors
|
wenzelm@4317
|
436 |
of~$thy$.
|
wenzelm@4317
|
437 |
|
wenzelm@4317
|
438 |
\item[\ttindexbold{ancestors_of} $thy$] returns all ancestors of~$thy$
|
wenzelm@4317
|
439 |
(not including $thy$ itself).
|
wenzelm@4317
|
440 |
|
wenzelm@4317
|
441 |
\item[\ttindexbold{sign_of} $thy$] returns the signature associated
|
wenzelm@4317
|
442 |
with~$thy$. It is useful with functions like {\tt
|
wenzelm@4317
|
443 |
read_instantiate_sg}, which take a signature as an argument.
|
wenzelm@4317
|
444 |
|
wenzelm@4317
|
445 |
\item[\ttindexbold{Sign.stamp_names_of} $sg$]\index{signatures}
|
wenzelm@4317
|
446 |
returns the names of the identification \rmindex{stamps} of ax
|
wenzelm@4317
|
447 |
signature. These coincide with the names of its full ancestry
|
wenzelm@4317
|
448 |
including that of $sg$ itself.
|
lcp@104
|
449 |
|
lcp@324
|
450 |
\end{ttdescription}
|
lcp@104
|
451 |
|
clasohm@1369
|
452 |
|
lcp@104
|
453 |
\section{Terms}
|
lcp@104
|
454 |
\index{terms|bold}
|
lcp@324
|
455 |
Terms belong to the \ML\ type \mltydx{term}, which is a concrete datatype
|
wenzelm@3108
|
456 |
with six constructors:
|
lcp@104
|
457 |
\begin{ttbox}
|
lcp@104
|
458 |
type indexname = string * int;
|
lcp@104
|
459 |
infix 9 $;
|
lcp@104
|
460 |
datatype term = Const of string * typ
|
lcp@104
|
461 |
| Free of string * typ
|
lcp@104
|
462 |
| Var of indexname * typ
|
lcp@104
|
463 |
| Bound of int
|
lcp@104
|
464 |
| Abs of string * typ * term
|
lcp@104
|
465 |
| op $ of term * term;
|
lcp@104
|
466 |
\end{ttbox}
|
lcp@324
|
467 |
\begin{ttdescription}
|
wenzelm@4317
|
468 |
\item[\ttindexbold{Const} ($a$, $T$)] \index{constants|bold}
|
lcp@286
|
469 |
is the {\bf constant} with name~$a$ and type~$T$. Constants include
|
lcp@286
|
470 |
connectives like $\land$ and $\forall$ as well as constants like~0
|
lcp@286
|
471 |
and~$Suc$. Other constants may be required to define a logic's concrete
|
wenzelm@864
|
472 |
syntax.
|
lcp@104
|
473 |
|
wenzelm@4317
|
474 |
\item[\ttindexbold{Free} ($a$, $T$)] \index{variables!free|bold}
|
lcp@324
|
475 |
is the {\bf free variable} with name~$a$ and type~$T$.
|
lcp@104
|
476 |
|
wenzelm@4317
|
477 |
\item[\ttindexbold{Var} ($v$, $T$)] \index{unknowns|bold}
|
lcp@324
|
478 |
is the {\bf scheme variable} with indexname~$v$ and type~$T$. An
|
lcp@324
|
479 |
\mltydx{indexname} is a string paired with a non-negative index, or
|
lcp@324
|
480 |
subscript; a term's scheme variables can be systematically renamed by
|
lcp@324
|
481 |
incrementing their subscripts. Scheme variables are essentially free
|
lcp@324
|
482 |
variables, but may be instantiated during unification.
|
lcp@104
|
483 |
|
lcp@324
|
484 |
\item[\ttindexbold{Bound} $i$] \index{variables!bound|bold}
|
lcp@324
|
485 |
is the {\bf bound variable} with de Bruijn index~$i$, which counts the
|
lcp@324
|
486 |
number of lambdas, starting from zero, between a variable's occurrence
|
lcp@324
|
487 |
and its binding. The representation prevents capture of variables. For
|
lcp@324
|
488 |
more information see de Bruijn \cite{debruijn72} or
|
lcp@324
|
489 |
Paulson~\cite[page~336]{paulson91}.
|
lcp@104
|
490 |
|
wenzelm@4317
|
491 |
\item[\ttindexbold{Abs} ($a$, $T$, $u$)]
|
lcp@324
|
492 |
\index{lambda abs@$\lambda$-abstractions|bold}
|
lcp@324
|
493 |
is the $\lambda$-{\bf abstraction} with body~$u$, and whose bound
|
lcp@324
|
494 |
variable has name~$a$ and type~$T$. The name is used only for parsing
|
lcp@324
|
495 |
and printing; it has no logical significance.
|
lcp@104
|
496 |
|
lcp@324
|
497 |
\item[$t$ \$ $u$] \index{$@{\tt\$}|bold} \index{function applications|bold}
|
wenzelm@864
|
498 |
is the {\bf application} of~$t$ to~$u$.
|
lcp@324
|
499 |
\end{ttdescription}
|
lcp@286
|
500 |
Application is written as an infix operator to aid readability.
|
lcp@332
|
501 |
Here is an \ML\ pattern to recognize \FOL{} formulae of
|
lcp@104
|
502 |
the form~$A\imp B$, binding the subformulae to~$A$ and~$B$:
|
wenzelm@864
|
503 |
\begin{ttbox}
|
lcp@104
|
504 |
Const("Trueprop",_) $ (Const("op -->",_) $ A $ B)
|
lcp@104
|
505 |
\end{ttbox}
|
lcp@104
|
506 |
|
lcp@104
|
507 |
|
wenzelm@4317
|
508 |
\section{*Variable binding}
|
lcp@286
|
509 |
\begin{ttbox}
|
lcp@286
|
510 |
loose_bnos : term -> int list
|
lcp@286
|
511 |
incr_boundvars : int -> term -> term
|
lcp@286
|
512 |
abstract_over : term*term -> term
|
lcp@286
|
513 |
variant_abs : string * typ * term -> string * term
|
wenzelm@4374
|
514 |
aconv : term * term -> bool\hfill{\bf infix}
|
lcp@286
|
515 |
\end{ttbox}
|
lcp@286
|
516 |
These functions are all concerned with the de Bruijn representation of
|
lcp@286
|
517 |
bound variables.
|
lcp@324
|
518 |
\begin{ttdescription}
|
wenzelm@864
|
519 |
\item[\ttindexbold{loose_bnos} $t$]
|
lcp@286
|
520 |
returns the list of all dangling bound variable references. In
|
lcp@286
|
521 |
particular, {\tt Bound~0} is loose unless it is enclosed in an
|
lcp@286
|
522 |
abstraction. Similarly {\tt Bound~1} is loose unless it is enclosed in
|
lcp@286
|
523 |
at least two abstractions; if enclosed in just one, the list will contain
|
lcp@286
|
524 |
the number 0. A well-formed term does not contain any loose variables.
|
lcp@286
|
525 |
|
wenzelm@864
|
526 |
\item[\ttindexbold{incr_boundvars} $j$]
|
lcp@332
|
527 |
increases a term's dangling bound variables by the offset~$j$. This is
|
lcp@286
|
528 |
required when moving a subterm into a context where it is enclosed by a
|
lcp@286
|
529 |
different number of abstractions. Bound variables with a matching
|
lcp@286
|
530 |
abstraction are unaffected.
|
lcp@286
|
531 |
|
wenzelm@864
|
532 |
\item[\ttindexbold{abstract_over} $(v,t)$]
|
lcp@286
|
533 |
forms the abstraction of~$t$ over~$v$, which may be any well-formed term.
|
lcp@286
|
534 |
It replaces every occurrence of \(v\) by a {\tt Bound} variable with the
|
lcp@286
|
535 |
correct index.
|
lcp@286
|
536 |
|
wenzelm@864
|
537 |
\item[\ttindexbold{variant_abs} $(a,T,u)$]
|
lcp@286
|
538 |
substitutes into $u$, which should be the body of an abstraction.
|
lcp@286
|
539 |
It replaces each occurrence of the outermost bound variable by a free
|
lcp@286
|
540 |
variable. The free variable has type~$T$ and its name is a variant
|
lcp@332
|
541 |
of~$a$ chosen to be distinct from all constants and from all variables
|
lcp@286
|
542 |
free in~$u$.
|
lcp@286
|
543 |
|
wenzelm@864
|
544 |
\item[$t$ \ttindexbold{aconv} $u$]
|
lcp@286
|
545 |
tests whether terms~$t$ and~$u$ are \(\alpha\)-convertible: identical up
|
lcp@286
|
546 |
to renaming of bound variables.
|
lcp@286
|
547 |
\begin{itemize}
|
lcp@286
|
548 |
\item
|
lcp@286
|
549 |
Two constants, {\tt Free}s, or {\tt Var}s are \(\alpha\)-convertible
|
lcp@286
|
550 |
if their names and types are equal.
|
lcp@286
|
551 |
(Variables having the same name but different types are thus distinct.
|
lcp@286
|
552 |
This confusing situation should be avoided!)
|
lcp@286
|
553 |
\item
|
lcp@286
|
554 |
Two bound variables are \(\alpha\)-convertible
|
lcp@286
|
555 |
if they have the same number.
|
lcp@286
|
556 |
\item
|
lcp@286
|
557 |
Two abstractions are \(\alpha\)-convertible
|
lcp@286
|
558 |
if their bodies are, and their bound variables have the same type.
|
lcp@286
|
559 |
\item
|
lcp@286
|
560 |
Two applications are \(\alpha\)-convertible
|
lcp@286
|
561 |
if the corresponding subterms are.
|
lcp@286
|
562 |
\end{itemize}
|
lcp@286
|
563 |
|
lcp@324
|
564 |
\end{ttdescription}
|
lcp@286
|
565 |
|
wenzelm@864
|
566 |
\section{Certified terms}\index{terms!certified|bold}\index{signatures}
|
wenzelm@864
|
567 |
A term $t$ can be {\bf certified} under a signature to ensure that every type
|
wenzelm@864
|
568 |
in~$t$ is well-formed and every constant in~$t$ is a type instance of a
|
wenzelm@864
|
569 |
constant declared in the signature. The term must be well-typed and its use
|
wenzelm@864
|
570 |
of bound variables must be well-formed. Meta-rules such as {\tt forall_elim}
|
wenzelm@864
|
571 |
take certified terms as arguments.
|
lcp@104
|
572 |
|
lcp@324
|
573 |
Certified terms belong to the abstract type \mltydx{cterm}.
|
lcp@104
|
574 |
Elements of the type can only be created through the certification process.
|
lcp@104
|
575 |
In case of error, Isabelle raises exception~\ttindex{TERM}\@.
|
lcp@104
|
576 |
|
lcp@104
|
577 |
\subsection{Printing terms}
|
lcp@324
|
578 |
\index{terms!printing of}
|
wenzelm@864
|
579 |
\begin{ttbox}
|
nipkow@275
|
580 |
string_of_cterm : cterm -> string
|
lcp@104
|
581 |
Sign.string_of_term : Sign.sg -> term -> string
|
lcp@104
|
582 |
\end{ttbox}
|
lcp@324
|
583 |
\begin{ttdescription}
|
wenzelm@864
|
584 |
\item[\ttindexbold{string_of_cterm} $ct$]
|
lcp@104
|
585 |
displays $ct$ as a string.
|
lcp@104
|
586 |
|
wenzelm@864
|
587 |
\item[\ttindexbold{Sign.string_of_term} $sign$ $t$]
|
lcp@104
|
588 |
displays $t$ as a string, using the syntax of~$sign$.
|
lcp@324
|
589 |
\end{ttdescription}
|
lcp@104
|
590 |
|
lcp@104
|
591 |
\subsection{Making and inspecting certified terms}
|
wenzelm@864
|
592 |
\begin{ttbox}
|
wenzelm@4543
|
593 |
cterm_of : Sign.sg -> term -> cterm
|
wenzelm@4543
|
594 |
read_cterm : Sign.sg -> string * typ -> cterm
|
wenzelm@4543
|
595 |
cert_axm : Sign.sg -> string * term -> string * term
|
wenzelm@4543
|
596 |
read_axm : Sign.sg -> string * string -> string * term
|
wenzelm@4543
|
597 |
rep_cterm : cterm -> {\ttlbrace}T:typ, t:term, sign:Sign.sg, maxidx:int\ttrbrace
|
wenzelm@4543
|
598 |
Sign.certify_term : Sign.sg -> term -> term * typ * int
|
lcp@104
|
599 |
\end{ttbox}
|
lcp@324
|
600 |
\begin{ttdescription}
|
wenzelm@4543
|
601 |
|
wenzelm@4543
|
602 |
\item[\ttindexbold{cterm_of} $sign$ $t$] \index{signatures} certifies
|
wenzelm@4543
|
603 |
$t$ with respect to signature~$sign$.
|
wenzelm@4543
|
604 |
|
wenzelm@4543
|
605 |
\item[\ttindexbold{read_cterm} $sign$ ($s$, $T$)] reads the string~$s$
|
wenzelm@4543
|
606 |
using the syntax of~$sign$, creating a certified term. The term is
|
wenzelm@4543
|
607 |
checked to have type~$T$; this type also tells the parser what kind
|
wenzelm@4543
|
608 |
of phrase to parse.
|
wenzelm@4543
|
609 |
|
wenzelm@4543
|
610 |
\item[\ttindexbold{cert_axm} $sign$ ($name$, $t$)] certifies $t$ with
|
wenzelm@4543
|
611 |
respect to $sign$ as a meta-proposition and converts all exceptions
|
wenzelm@4543
|
612 |
to an error, including the final message
|
wenzelm@864
|
613 |
\begin{ttbox}
|
wenzelm@864
|
614 |
The error(s) above occurred in axiom "\(name\)"
|
wenzelm@864
|
615 |
\end{ttbox}
|
wenzelm@864
|
616 |
|
wenzelm@4543
|
617 |
\item[\ttindexbold{read_axm} $sign$ ($name$, $s$)] similar to {\tt
|
wenzelm@4543
|
618 |
cert_axm}, but first reads the string $s$ using the syntax of
|
wenzelm@4543
|
619 |
$sign$.
|
wenzelm@4543
|
620 |
|
wenzelm@4543
|
621 |
\item[\ttindexbold{rep_cterm} $ct$] decomposes $ct$ as a record
|
wenzelm@4543
|
622 |
containing its type, the term itself, its signature, and the maximum
|
wenzelm@4543
|
623 |
subscript of its unknowns. The type and maximum subscript are
|
wenzelm@4543
|
624 |
computed during certification.
|
wenzelm@4543
|
625 |
|
wenzelm@4543
|
626 |
\item[\ttindexbold{Sign.certify_term}] is a more primitive version of
|
wenzelm@4543
|
627 |
\texttt{cterm_of}, returning the internal representation instead of
|
wenzelm@4543
|
628 |
an abstract \texttt{cterm}.
|
wenzelm@864
|
629 |
|
lcp@324
|
630 |
\end{ttdescription}
|
lcp@104
|
631 |
|
lcp@104
|
632 |
|
wenzelm@864
|
633 |
\section{Types}\index{types|bold}
|
wenzelm@864
|
634 |
Types belong to the \ML\ type \mltydx{typ}, which is a concrete datatype with
|
wenzelm@864
|
635 |
three constructor functions. These correspond to type constructors, free
|
wenzelm@864
|
636 |
type variables and schematic type variables. Types are classified by sorts,
|
wenzelm@864
|
637 |
which are lists of classes (representing an intersection). A class is
|
wenzelm@864
|
638 |
represented by a string.
|
lcp@104
|
639 |
\begin{ttbox}
|
lcp@104
|
640 |
type class = string;
|
lcp@104
|
641 |
type sort = class list;
|
lcp@104
|
642 |
|
lcp@104
|
643 |
datatype typ = Type of string * typ list
|
lcp@104
|
644 |
| TFree of string * sort
|
lcp@104
|
645 |
| TVar of indexname * sort;
|
lcp@104
|
646 |
|
lcp@104
|
647 |
infixr 5 -->;
|
wenzelm@864
|
648 |
fun S --> T = Type ("fun", [S, T]);
|
lcp@104
|
649 |
\end{ttbox}
|
lcp@324
|
650 |
\begin{ttdescription}
|
wenzelm@4317
|
651 |
\item[\ttindexbold{Type} ($a$, $Ts$)] \index{type constructors|bold}
|
lcp@324
|
652 |
applies the {\bf type constructor} named~$a$ to the type operands~$Ts$.
|
lcp@324
|
653 |
Type constructors include~\tydx{fun}, the binary function space
|
lcp@324
|
654 |
constructor, as well as nullary type constructors such as~\tydx{prop}.
|
lcp@324
|
655 |
Other type constructors may be introduced. In expressions, but not in
|
lcp@324
|
656 |
patterns, \hbox{\tt$S$-->$T$} is a convenient shorthand for function
|
lcp@324
|
657 |
types.
|
lcp@104
|
658 |
|
wenzelm@4317
|
659 |
\item[\ttindexbold{TFree} ($a$, $s$)] \index{type variables|bold}
|
lcp@324
|
660 |
is the {\bf type variable} with name~$a$ and sort~$s$.
|
lcp@104
|
661 |
|
wenzelm@4317
|
662 |
\item[\ttindexbold{TVar} ($v$, $s$)] \index{type unknowns|bold}
|
lcp@324
|
663 |
is the {\bf type unknown} with indexname~$v$ and sort~$s$.
|
lcp@324
|
664 |
Type unknowns are essentially free type variables, but may be
|
lcp@324
|
665 |
instantiated during unification.
|
lcp@324
|
666 |
\end{ttdescription}
|
lcp@104
|
667 |
|
lcp@104
|
668 |
|
lcp@104
|
669 |
\section{Certified types}
|
lcp@104
|
670 |
\index{types!certified|bold}
|
wenzelm@864
|
671 |
Certified types, which are analogous to certified terms, have type
|
nipkow@275
|
672 |
\ttindexbold{ctyp}.
|
lcp@104
|
673 |
|
lcp@104
|
674 |
\subsection{Printing types}
|
lcp@324
|
675 |
\index{types!printing of}
|
wenzelm@864
|
676 |
\begin{ttbox}
|
nipkow@275
|
677 |
string_of_ctyp : ctyp -> string
|
lcp@104
|
678 |
Sign.string_of_typ : Sign.sg -> typ -> string
|
lcp@104
|
679 |
\end{ttbox}
|
lcp@324
|
680 |
\begin{ttdescription}
|
wenzelm@864
|
681 |
\item[\ttindexbold{string_of_ctyp} $cT$]
|
lcp@104
|
682 |
displays $cT$ as a string.
|
lcp@104
|
683 |
|
wenzelm@864
|
684 |
\item[\ttindexbold{Sign.string_of_typ} $sign$ $T$]
|
lcp@104
|
685 |
displays $T$ as a string, using the syntax of~$sign$.
|
lcp@324
|
686 |
\end{ttdescription}
|
lcp@104
|
687 |
|
lcp@104
|
688 |
|
lcp@104
|
689 |
\subsection{Making and inspecting certified types}
|
wenzelm@864
|
690 |
\begin{ttbox}
|
wenzelm@4543
|
691 |
ctyp_of : Sign.sg -> typ -> ctyp
|
wenzelm@4543
|
692 |
rep_ctyp : ctyp -> {\ttlbrace}T: typ, sign: Sign.sg\ttrbrace
|
wenzelm@4543
|
693 |
Sign.certify_typ : Sign.sg -> typ -> typ
|
lcp@104
|
694 |
\end{ttbox}
|
lcp@324
|
695 |
\begin{ttdescription}
|
wenzelm@4543
|
696 |
|
wenzelm@4543
|
697 |
\item[\ttindexbold{ctyp_of} $sign$ $T$] \index{signatures} certifies
|
wenzelm@4543
|
698 |
$T$ with respect to signature~$sign$.
|
wenzelm@4543
|
699 |
|
wenzelm@4543
|
700 |
\item[\ttindexbold{rep_ctyp} $cT$] decomposes $cT$ as a record
|
wenzelm@4543
|
701 |
containing the type itself and its signature.
|
wenzelm@4543
|
702 |
|
wenzelm@4543
|
703 |
\item[\ttindexbold{Sign.certify_typ}] is a more primitive version of
|
wenzelm@4543
|
704 |
\texttt{ctyp_of}, returning the internal representation instead of
|
wenzelm@4543
|
705 |
an abstract \texttt{ctyp}.
|
lcp@104
|
706 |
|
lcp@324
|
707 |
\end{ttdescription}
|
lcp@104
|
708 |
|
paulson@1846
|
709 |
|
wenzelm@4317
|
710 |
\section{Oracles: calling trusted external reasoners}
|
paulson@1846
|
711 |
\label{sec:oracles}
|
paulson@1846
|
712 |
\index{oracles|(}
|
paulson@1846
|
713 |
|
paulson@1846
|
714 |
Oracles allow Isabelle to take advantage of external reasoners such as
|
paulson@1846
|
715 |
arithmetic decision procedures, model checkers, fast tautology checkers or
|
paulson@1846
|
716 |
computer algebra systems. Invoked as an oracle, an external reasoner can
|
paulson@1846
|
717 |
create arbitrary Isabelle theorems. It is your responsibility to ensure that
|
paulson@1846
|
718 |
the external reasoner is as trustworthy as your application requires.
|
paulson@1846
|
719 |
Isabelle's proof objects~(\S\ref{sec:proofObjects}) record how each theorem
|
paulson@1846
|
720 |
depends upon oracle calls.
|
paulson@1846
|
721 |
|
paulson@1846
|
722 |
\begin{ttbox}
|
wenzelm@4317
|
723 |
invoke_oracle : theory -> xstring -> Sign.sg * object -> thm
|
paulson@4597
|
724 |
Theory.add_oracle : bstring * (Sign.sg * object -> term) -> theory
|
paulson@4597
|
725 |
-> theory
|
paulson@1846
|
726 |
\end{ttbox}
|
paulson@1846
|
727 |
\begin{ttdescription}
|
wenzelm@4317
|
728 |
\item[\ttindexbold{invoke_oracle} $thy$ $name$ ($sign$, $data$)]
|
wenzelm@4317
|
729 |
invokes the oracle $name$ of theory $thy$ passing the information
|
wenzelm@4317
|
730 |
contained in the exception value $data$ and creating a theorem
|
wenzelm@4317
|
731 |
having signature $sign$. Note that type \ttindex{object} is just an
|
wenzelm@4317
|
732 |
abbreviation for \texttt{exn}. Errors arise if $thy$ does not have
|
wenzelm@4317
|
733 |
an oracle called $name$, if the oracle rejects its arguments or if
|
wenzelm@4317
|
734 |
its result is ill-typed.
|
wenzelm@4317
|
735 |
|
wenzelm@4317
|
736 |
\item[\ttindexbold{Theory.add_oracle} $name$ $fun$ $thy$] extends
|
wenzelm@4317
|
737 |
$thy$ by oracle $fun$ called $name$. It is seldom called
|
wenzelm@4317
|
738 |
explicitly, as there is concrete syntax for oracles in theory files.
|
paulson@1846
|
739 |
\end{ttdescription}
|
paulson@1846
|
740 |
|
paulson@1846
|
741 |
A curious feature of {\ML} exceptions is that they are ordinary constructors.
|
paulson@1846
|
742 |
The {\ML} type {\tt exn} is a datatype that can be extended at any time. (See
|
paulson@1846
|
743 |
my {\em {ML} for the Working Programmer}~\cite{paulson-ml2}, especially
|
paulson@1846
|
744 |
page~136.) The oracle mechanism takes advantage of this to allow an oracle to
|
paulson@1846
|
745 |
take any information whatever.
|
paulson@1846
|
746 |
|
paulson@1846
|
747 |
There must be some way of invoking the external reasoner from \ML, either
|
paulson@1846
|
748 |
because it is coded in {\ML} or via an operating system interface. Isabelle
|
paulson@1846
|
749 |
expects the {\ML} function to take two arguments: a signature and an
|
wenzelm@4317
|
750 |
exception object.
|
paulson@1846
|
751 |
\begin{itemize}
|
paulson@1846
|
752 |
\item The signature will typically be that of a desendant of the theory
|
paulson@1846
|
753 |
declaring the oracle. The oracle will use it to distinguish constants from
|
paulson@1846
|
754 |
variables, etc., and it will be attached to the generated theorems.
|
paulson@1846
|
755 |
|
paulson@1846
|
756 |
\item The exception is used to pass arbitrary information to the oracle. This
|
paulson@1846
|
757 |
information must contain a full description of the problem to be solved by
|
paulson@1846
|
758 |
the external reasoner, including any additional information that might be
|
paulson@1846
|
759 |
required. The oracle may raise the exception to indicate that it cannot
|
paulson@1846
|
760 |
solve the specified problem.
|
paulson@1846
|
761 |
\end{itemize}
|
paulson@1846
|
762 |
|
wenzelm@4317
|
763 |
A trivial example is provided in theory {\tt FOL/ex/IffOracle}. This
|
wenzelm@4317
|
764 |
oracle generates tautologies of the form $P\bimp\cdots\bimp P$, with
|
wenzelm@4317
|
765 |
an even number of $P$s.
|
paulson@1846
|
766 |
|
wenzelm@4317
|
767 |
The \texttt{ML} section of \texttt{IffOracle.thy} begins by declaring
|
wenzelm@4317
|
768 |
a few auxiliary functions (suppressed below) for creating the
|
wenzelm@4317
|
769 |
tautologies. Then it declares a new exception constructor for the
|
wenzelm@4317
|
770 |
information required by the oracle: here, just an integer. It finally
|
wenzelm@4317
|
771 |
defines the oracle function itself.
|
paulson@1846
|
772 |
\begin{ttbox}
|
wenzelm@4317
|
773 |
exception IffOracleExn of int;\medskip
|
wenzelm@4317
|
774 |
fun mk_iff_oracle (sign, IffOracleExn n) =
|
wenzelm@4317
|
775 |
if n > 0 andalso n mod 2 = 0
|
wenzelm@4317
|
776 |
then Trueprop $ mk_iff n
|
wenzelm@4317
|
777 |
else raise IffOracleExn n;
|
paulson@1846
|
778 |
\end{ttbox}
|
wenzelm@4317
|
779 |
Observe the function's two arguments, the signature {\tt sign} and the
|
wenzelm@4317
|
780 |
exception given as a pattern. The function checks its argument for
|
wenzelm@4317
|
781 |
validity. If $n$ is positive and even then it creates a tautology
|
wenzelm@4317
|
782 |
containing $n$ occurrences of~$P$. Otherwise it signals error by
|
wenzelm@4317
|
783 |
raising its own exception (just by happy coincidence). Errors may be
|
wenzelm@4317
|
784 |
signalled by other means, such as returning the theorem {\tt True}.
|
wenzelm@4317
|
785 |
Please ensure that the oracle's result is correctly typed; Isabelle
|
wenzelm@4317
|
786 |
will reject ill-typed theorems by raising a cryptic exception at top
|
wenzelm@4317
|
787 |
level.
|
paulson@1846
|
788 |
|
wenzelm@4317
|
789 |
The \texttt{oracle} section of {\tt IffOracle.thy} installs above
|
wenzelm@4317
|
790 |
\texttt{ML} function as follows:
|
paulson@1846
|
791 |
\begin{ttbox}
|
wenzelm@4317
|
792 |
IffOracle = FOL +\medskip
|
wenzelm@4317
|
793 |
oracle
|
wenzelm@4317
|
794 |
iff = mk_iff_oracle\medskip
|
paulson@1846
|
795 |
end
|
paulson@1846
|
796 |
\end{ttbox}
|
paulson@1846
|
797 |
|
wenzelm@4317
|
798 |
Now in \texttt{IffOracle.ML} we first define a wrapper for invoking
|
wenzelm@4317
|
799 |
the oracle:
|
paulson@1846
|
800 |
\begin{ttbox}
|
paulson@4597
|
801 |
fun iff_oracle n = invoke_oracle IffOracle.thy "iff"
|
paulson@4597
|
802 |
(sign_of IffOracle.thy, IffOracleExn n);
|
wenzelm@4317
|
803 |
\end{ttbox}
|
wenzelm@4317
|
804 |
|
wenzelm@4317
|
805 |
Here are some example applications of the \texttt{iff} oracle. An
|
wenzelm@4317
|
806 |
argument of 10 is allowed, but one of 5 is forbidden:
|
wenzelm@4317
|
807 |
\begin{ttbox}
|
wenzelm@4317
|
808 |
iff_oracle 10;
|
paulson@1846
|
809 |
{\out "P <-> P <-> P <-> P <-> P <-> P <-> P <-> P <-> P <-> P" : thm}
|
wenzelm@4317
|
810 |
iff_oracle 5;
|
paulson@1846
|
811 |
{\out Exception- IffOracleExn 5 raised}
|
paulson@1846
|
812 |
\end{ttbox}
|
paulson@1846
|
813 |
|
paulson@1846
|
814 |
\index{oracles|)}
|
lcp@104
|
815 |
\index{theories|)}
|
wenzelm@5369
|
816 |
|
wenzelm@5369
|
817 |
|
wenzelm@5369
|
818 |
%%% Local Variables:
|
wenzelm@5369
|
819 |
%%% mode: latex
|
wenzelm@5369
|
820 |
%%% TeX-master: "ref"
|
wenzelm@5369
|
821 |
%%% End:
|