--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/doc-src/IsarImplementation/Thy/Prelim.thy Mon Feb 16 20:47:44 2009 +0100
@@ -0,0 +1,778 @@
+theory Prelim
+imports Base
+begin
+
+chapter {* Preliminaries *}
+
+section {* Contexts \label{sec:context} *}
+
+text {*
+ A logical context represents the background that is required for
+ formulating statements and composing proofs. It acts as a medium to
+ produce formal content, depending on earlier material (declarations,
+ results etc.).
+
+ For example, derivations within the Isabelle/Pure logic can be
+ described as a judgment @{text "\<Gamma> \<turnstile>\<^sub>\<Theta> \<phi>"}, which means that a
+ proposition @{text "\<phi>"} is derivable from hypotheses @{text "\<Gamma>"}
+ within the theory @{text "\<Theta>"}. There are logical reasons for
+ keeping @{text "\<Theta>"} and @{text "\<Gamma>"} separate: theories can be
+ liberal about supporting type constructors and schematic
+ polymorphism of constants and axioms, while the inner calculus of
+ @{text "\<Gamma> \<turnstile> \<phi>"} is strictly limited to Simple Type Theory (with
+ fixed type variables in the assumptions).
+
+ \medskip Contexts and derivations are linked by the following key
+ principles:
+
+ \begin{itemize}
+
+ \item Transfer: monotonicity of derivations admits results to be
+ transferred into a \emph{larger} context, i.e.\ @{text "\<Gamma> \<turnstile>\<^sub>\<Theta>
+ \<phi>"} implies @{text "\<Gamma>' \<turnstile>\<^sub>\<Theta>\<^sub>' \<phi>"} for contexts @{text "\<Theta>'
+ \<supseteq> \<Theta>"} and @{text "\<Gamma>' \<supseteq> \<Gamma>"}.
+
+ \item Export: discharge of hypotheses admits results to be exported
+ into a \emph{smaller} context, i.e.\ @{text "\<Gamma>' \<turnstile>\<^sub>\<Theta> \<phi>"}
+ implies @{text "\<Gamma> \<turnstile>\<^sub>\<Theta> \<Delta> \<Longrightarrow> \<phi>"} where @{text "\<Gamma>' \<supseteq> \<Gamma>"} and
+ @{text "\<Delta> = \<Gamma>' - \<Gamma>"}. Note that @{text "\<Theta>"} remains unchanged here,
+ only the @{text "\<Gamma>"} part is affected.
+
+ \end{itemize}
+
+ \medskip By modeling the main characteristics of the primitive
+ @{text "\<Theta>"} and @{text "\<Gamma>"} above, and abstracting over any
+ particular logical content, we arrive at the fundamental notions of
+ \emph{theory context} and \emph{proof context} in Isabelle/Isar.
+ These implement a certain policy to manage arbitrary \emph{context
+ data}. There is a strongly-typed mechanism to declare new kinds of
+ data at compile time.
+
+ The internal bootstrap process of Isabelle/Pure eventually reaches a
+ stage where certain data slots provide the logical content of @{text
+ "\<Theta>"} and @{text "\<Gamma>"} sketched above, but this does not stop there!
+ Various additional data slots support all kinds of mechanisms that
+ are not necessarily part of the core logic.
+
+ For example, there would be data for canonical introduction and
+ elimination rules for arbitrary operators (depending on the
+ object-logic and application), which enables users to perform
+ standard proof steps implicitly (cf.\ the @{text "rule"} method
+ \cite{isabelle-isar-ref}).
+
+ \medskip Thus Isabelle/Isar is able to bring forth more and more
+ concepts successively. In particular, an object-logic like
+ Isabelle/HOL continues the Isabelle/Pure setup by adding specific
+ components for automated reasoning (classical reasoner, tableau
+ prover, structured induction etc.) and derived specification
+ mechanisms (inductive predicates, recursive functions etc.). All of
+ this is ultimately based on the generic data management by theory
+ and proof contexts introduced here.
+*}
+
+
+subsection {* Theory context \label{sec:context-theory} *}
+
+text {*
+ \glossary{Theory}{FIXME}
+
+ A \emph{theory} is a data container with explicit named and unique
+ identifier. Theories are related by a (nominal) sub-theory
+ relation, which corresponds to the dependency graph of the original
+ construction; each theory is derived from a certain sub-graph of
+ ancestor theories.
+
+ The @{text "merge"} operation produces the least upper bound of two
+ theories, which actually degenerates into absorption of one theory
+ into the other (due to the nominal sub-theory relation).
+
+ The @{text "begin"} operation starts a new theory by importing
+ several parent theories and entering a special @{text "draft"} mode,
+ which is sustained until the final @{text "end"} operation. A draft
+ theory acts like a linear type, where updates invalidate earlier
+ versions. An invalidated draft is called ``stale''.
+
+ The @{text "checkpoint"} operation produces an intermediate stepping
+ stone that will survive the next update: both the original and the
+ changed theory remain valid and are related by the sub-theory
+ relation. Checkpointing essentially recovers purely functional
+ theory values, at the expense of some extra internal bookkeeping.
+
+ The @{text "copy"} operation produces an auxiliary version that has
+ the same data content, but is unrelated to the original: updates of
+ the copy do not affect the original, neither does the sub-theory
+ relation hold.
+
+ \medskip The example in \figref{fig:ex-theory} below shows a theory
+ graph derived from @{text "Pure"}, with theory @{text "Length"}
+ importing @{text "Nat"} and @{text "List"}. The body of @{text
+ "Length"} consists of a sequence of updates, working mostly on
+ drafts. Intermediate checkpoints may occur as well, due to the
+ history mechanism provided by the Isar top-level, cf.\
+ \secref{sec:isar-toplevel}.
+
+ \begin{figure}[htb]
+ \begin{center}
+ \begin{tabular}{rcccl}
+ & & @{text "Pure"} \\
+ & & @{text "\<down>"} \\
+ & & @{text "FOL"} \\
+ & $\swarrow$ & & $\searrow$ & \\
+ @{text "Nat"} & & & & @{text "List"} \\
+ & $\searrow$ & & $\swarrow$ \\
+ & & @{text "Length"} \\
+ & & \multicolumn{3}{l}{~~@{keyword "imports"}} \\
+ & & \multicolumn{3}{l}{~~@{keyword "begin"}} \\
+ & & $\vdots$~~ \\
+ & & @{text "\<bullet>"}~~ \\
+ & & $\vdots$~~ \\
+ & & @{text "\<bullet>"}~~ \\
+ & & $\vdots$~~ \\
+ & & \multicolumn{3}{l}{~~@{command "end"}} \\
+ \end{tabular}
+ \caption{A theory definition depending on ancestors}\label{fig:ex-theory}
+ \end{center}
+ \end{figure}
+
+ \medskip There is a separate notion of \emph{theory reference} for
+ maintaining a live link to an evolving theory context: updates on
+ drafts are propagated automatically. Dynamic updating stops after
+ an explicit @{text "end"} only.
+
+ Derived entities may store a theory reference in order to indicate
+ the context they belong to. This implicitly assumes monotonic
+ reasoning, because the referenced context may become larger without
+ further notice.
+*}
+
+text %mlref {*
+ \begin{mldecls}
+ @{index_ML_type theory} \\
+ @{index_ML Theory.subthy: "theory * theory -> bool"} \\
+ @{index_ML Theory.merge: "theory * theory -> theory"} \\
+ @{index_ML Theory.checkpoint: "theory -> theory"} \\
+ @{index_ML Theory.copy: "theory -> theory"} \\
+ \end{mldecls}
+ \begin{mldecls}
+ @{index_ML_type theory_ref} \\
+ @{index_ML Theory.deref: "theory_ref -> theory"} \\
+ @{index_ML Theory.check_thy: "theory -> theory_ref"} \\
+ \end{mldecls}
+
+ \begin{description}
+
+ \item @{ML_type theory} represents theory contexts. This is
+ essentially a linear type! Most operations destroy the original
+ version, which then becomes ``stale''.
+
+ \item @{ML "Theory.subthy"}~@{text "(thy\<^sub>1, thy\<^sub>2)"}
+ compares theories according to the inherent graph structure of the
+ construction. This sub-theory relation is a nominal approximation
+ of inclusion (@{text "\<subseteq>"}) of the corresponding content.
+
+ \item @{ML "Theory.merge"}~@{text "(thy\<^sub>1, thy\<^sub>2)"}
+ absorbs one theory into the other. This fails for unrelated
+ theories!
+
+ \item @{ML "Theory.checkpoint"}~@{text "thy"} produces a safe
+ stepping stone in the linear development of @{text "thy"}. The next
+ update will result in two related, valid theories.
+
+ \item @{ML "Theory.copy"}~@{text "thy"} produces a variant of @{text
+ "thy"} that holds a copy of the same data. The result is not
+ related to the original; the original is unchanched.
+
+ \item @{ML_type theory_ref} represents a sliding reference to an
+ always valid theory; updates on the original are propagated
+ automatically.
+
+ \item @{ML "Theory.deref"}~@{text "thy_ref"} turns a @{ML_type
+ "theory_ref"} into an @{ML_type "theory"} value. As the referenced
+ theory evolves monotonically over time, later invocations of @{ML
+ "Theory.deref"} may refer to a larger context.
+
+ \item @{ML "Theory.check_thy"}~@{text "thy"} produces a @{ML_type
+ "theory_ref"} from a valid @{ML_type "theory"} value.
+
+ \end{description}
+*}
+
+
+subsection {* Proof context \label{sec:context-proof} *}
+
+text {*
+ \glossary{Proof context}{The static context of a structured proof,
+ acts like a local ``theory'' of the current portion of Isar proof
+ text, generalizes the idea of local hypotheses @{text "\<Gamma>"} in
+ judgments @{text "\<Gamma> \<turnstile> \<phi>"} of natural deduction calculi. There is a
+ generic notion of introducing and discharging hypotheses.
+ Arbritrary auxiliary context data may be adjoined.}
+
+ A proof context is a container for pure data with a back-reference
+ to the theory it belongs to. The @{text "init"} operation creates a
+ proof context from a given theory. Modifications to draft theories
+ are propagated to the proof context as usual, but there is also an
+ explicit @{text "transfer"} operation to force resynchronization
+ with more substantial updates to the underlying theory. The actual
+ context data does not require any special bookkeeping, thanks to the
+ lack of destructive features.
+
+ Entities derived in a proof context need to record inherent logical
+ requirements explicitly, since there is no separate context
+ identification as for theories. For example, hypotheses used in
+ primitive derivations (cf.\ \secref{sec:thms}) are recorded
+ separately within the sequent @{text "\<Gamma> \<turnstile> \<phi>"}, just to make double
+ sure. Results could still leak into an alien proof context do to
+ programming errors, but Isabelle/Isar includes some extra validity
+ checks in critical positions, notably at the end of a sub-proof.
+
+ Proof contexts may be manipulated arbitrarily, although the common
+ discipline is to follow block structure as a mental model: a given
+ context is extended consecutively, and results are exported back
+ into the original context. Note that the Isar proof states model
+ block-structured reasoning explicitly, using a stack of proof
+ contexts internally, cf.\ \secref{sec:isar-proof-state}.
+*}
+
+text %mlref {*
+ \begin{mldecls}
+ @{index_ML_type Proof.context} \\
+ @{index_ML ProofContext.init: "theory -> Proof.context"} \\
+ @{index_ML ProofContext.theory_of: "Proof.context -> theory"} \\
+ @{index_ML ProofContext.transfer: "theory -> Proof.context -> Proof.context"} \\
+ \end{mldecls}
+
+ \begin{description}
+
+ \item @{ML_type Proof.context} represents proof contexts. Elements
+ of this type are essentially pure values, with a sliding reference
+ to the background theory.
+
+ \item @{ML ProofContext.init}~@{text "thy"} produces a proof context
+ derived from @{text "thy"}, initializing all data.
+
+ \item @{ML ProofContext.theory_of}~@{text "ctxt"} selects the
+ background theory from @{text "ctxt"}, dereferencing its internal
+ @{ML_type theory_ref}.
+
+ \item @{ML ProofContext.transfer}~@{text "thy ctxt"} promotes the
+ background theory of @{text "ctxt"} to the super theory @{text
+ "thy"}.
+
+ \end{description}
+*}
+
+
+subsection {* Generic contexts \label{sec:generic-context} *}
+
+text {*
+ A generic context is the disjoint sum of either a theory or proof
+ context. Occasionally, this enables uniform treatment of generic
+ context data, typically extra-logical information. Operations on
+ generic contexts include the usual injections, partial selections,
+ and combinators for lifting operations on either component of the
+ disjoint sum.
+
+ Moreover, there are total operations @{text "theory_of"} and @{text
+ "proof_of"} to convert a generic context into either kind: a theory
+ can always be selected from the sum, while a proof context might
+ have to be constructed by an ad-hoc @{text "init"} operation.
+*}
+
+text %mlref {*
+ \begin{mldecls}
+ @{index_ML_type Context.generic} \\
+ @{index_ML Context.theory_of: "Context.generic -> theory"} \\
+ @{index_ML Context.proof_of: "Context.generic -> Proof.context"} \\
+ \end{mldecls}
+
+ \begin{description}
+
+ \item @{ML_type Context.generic} is the direct sum of @{ML_type
+ "theory"} and @{ML_type "Proof.context"}, with the datatype
+ constructors @{ML "Context.Theory"} and @{ML "Context.Proof"}.
+
+ \item @{ML Context.theory_of}~@{text "context"} always produces a
+ theory from the generic @{text "context"}, using @{ML
+ "ProofContext.theory_of"} as required.
+
+ \item @{ML Context.proof_of}~@{text "context"} always produces a
+ proof context from the generic @{text "context"}, using @{ML
+ "ProofContext.init"} as required (note that this re-initializes the
+ context data with each invocation).
+
+ \end{description}
+*}
+
+
+subsection {* Context data \label{sec:context-data} *}
+
+text {*
+ The main purpose of theory and proof contexts is to manage arbitrary
+ data. New data types can be declared incrementally at compile time.
+ There are separate declaration mechanisms for any of the three kinds
+ of contexts: theory, proof, generic.
+
+ \paragraph{Theory data} may refer to destructive entities, which are
+ maintained in direct correspondence to the linear evolution of
+ theory values, including explicit copies.\footnote{Most existing
+ instances of destructive theory data are merely historical relics
+ (e.g.\ the destructive theorem storage, and destructive hints for
+ the Simplifier and Classical rules).} A theory data declaration
+ needs to implement the following SML signature:
+
+ \medskip
+ \begin{tabular}{ll}
+ @{text "\<type> T"} & representing type \\
+ @{text "\<val> empty: T"} & empty default value \\
+ @{text "\<val> copy: T \<rightarrow> T"} & refresh impure data \\
+ @{text "\<val> extend: T \<rightarrow> T"} & re-initialize on import \\
+ @{text "\<val> merge: T \<times> T \<rightarrow> T"} & join on import \\
+ \end{tabular}
+ \medskip
+
+ \noindent The @{text "empty"} value acts as initial default for
+ \emph{any} theory that does not declare actual data content; @{text
+ "copy"} maintains persistent integrity for impure data, it is just
+ the identity for pure values; @{text "extend"} is acts like a
+ unitary version of @{text "merge"}, both operations should also
+ include the functionality of @{text "copy"} for impure data.
+
+ \paragraph{Proof context data} is purely functional. A declaration
+ needs to implement the following SML signature:
+
+ \medskip
+ \begin{tabular}{ll}
+ @{text "\<type> T"} & representing type \\
+ @{text "\<val> init: theory \<rightarrow> T"} & produce initial value \\
+ \end{tabular}
+ \medskip
+
+ \noindent The @{text "init"} operation is supposed to produce a pure
+ value from the given background theory.
+
+ \paragraph{Generic data} provides a hybrid interface for both theory
+ and proof data. The declaration is essentially the same as for
+ (pure) theory data, without @{text "copy"}. The @{text "init"}
+ operation for proof contexts merely selects the current data value
+ from the background theory.
+
+ \bigskip A data declaration of type @{text "T"} results in the
+ following interface:
+
+ \medskip
+ \begin{tabular}{ll}
+ @{text "init: theory \<rightarrow> theory"} \\
+ @{text "get: context \<rightarrow> T"} \\
+ @{text "put: T \<rightarrow> context \<rightarrow> context"} \\
+ @{text "map: (T \<rightarrow> T) \<rightarrow> context \<rightarrow> context"} \\
+ \end{tabular}
+ \medskip
+
+ \noindent Here @{text "init"} is only applicable to impure theory
+ data to install a fresh copy persistently (destructive update on
+ uninitialized has no permanent effect). The other operations provide
+ access for the particular kind of context (theory, proof, or generic
+ context). Note that this is a safe interface: there is no other way
+ to access the corresponding data slot of a context. By keeping
+ these operations private, a component may maintain abstract values
+ authentically, without other components interfering.
+*}
+
+text %mlref {*
+ \begin{mldecls}
+ @{index_ML_functor TheoryDataFun} \\
+ @{index_ML_functor ProofDataFun} \\
+ @{index_ML_functor GenericDataFun} \\
+ \end{mldecls}
+
+ \begin{description}
+
+ \item @{ML_functor TheoryDataFun}@{text "(spec)"} declares data for
+ type @{ML_type theory} according to the specification provided as
+ argument structure. The resulting structure provides data init and
+ access operations as described above.
+
+ \item @{ML_functor ProofDataFun}@{text "(spec)"} is analogous to
+ @{ML_functor TheoryDataFun} for type @{ML_type Proof.context}.
+
+ \item @{ML_functor GenericDataFun}@{text "(spec)"} is analogous to
+ @{ML_functor TheoryDataFun} for type @{ML_type Context.generic}.
+
+ \end{description}
+*}
+
+
+section {* Names \label{sec:names} *}
+
+text {*
+ In principle, a name is just a string, but there are various
+ convention for encoding additional structure. For example, ``@{text
+ "Foo.bar.baz"}'' is considered as a qualified name consisting of
+ three basic name components. The individual constituents of a name
+ may have further substructure, e.g.\ the string
+ ``\verb,\,\verb,<alpha>,'' encodes as a single symbol.
+*}
+
+
+subsection {* Strings of symbols *}
+
+text {*
+ \glossary{Symbol}{The smallest unit of text in Isabelle, subsumes
+ plain ASCII characters as well as an infinite collection of named
+ symbols (for greek, math etc.).}
+
+ A \emph{symbol} constitutes the smallest textual unit in Isabelle
+ --- raw characters are normally not encountered at all. Isabelle
+ strings consist of a sequence of symbols, represented as a packed
+ string or a list of strings. Each symbol is in itself a small
+ string, which has either one of the following forms:
+
+ \begin{enumerate}
+
+ \item a single ASCII character ``@{text "c"}'', for example
+ ``\verb,a,'',
+
+ \item a regular symbol ``\verb,\,\verb,<,@{text "ident"}\verb,>,'',
+ for example ``\verb,\,\verb,<alpha>,'',
+
+ \item a control symbol ``\verb,\,\verb,<^,@{text "ident"}\verb,>,'',
+ for example ``\verb,\,\verb,<^bold>,'',
+
+ \item a raw symbol ``\verb,\,\verb,<^raw:,@{text text}\verb,>,''
+ where @{text text} constists of printable characters excluding
+ ``\verb,.,'' and ``\verb,>,'', for example
+ ``\verb,\,\verb,<^raw:$\sum_{i = 1}^n$>,'',
+
+ \item a numbered raw control symbol ``\verb,\,\verb,<^raw,@{text
+ n}\verb,>, where @{text n} consists of digits, for example
+ ``\verb,\,\verb,<^raw42>,''.
+
+ \end{enumerate}
+
+ \noindent The @{text "ident"} syntax for symbol names is @{text
+ "letter (letter | digit)\<^sup>*"}, where @{text "letter =
+ A..Za..z"} and @{text "digit = 0..9"}. There are infinitely many
+ regular symbols and control symbols, but a fixed collection of
+ standard symbols is treated specifically. For example,
+ ``\verb,\,\verb,<alpha>,'' is classified as a letter, which means it
+ may occur within regular Isabelle identifiers.
+
+ Since the character set underlying Isabelle symbols is 7-bit ASCII
+ and 8-bit characters are passed through transparently, Isabelle may
+ also process Unicode/UCS data in UTF-8 encoding. Unicode provides
+ its own collection of mathematical symbols, but there is no built-in
+ link to the standard collection of Isabelle.
+
+ \medskip Output of Isabelle symbols depends on the print mode
+ (\secref{FIXME}). For example, the standard {\LaTeX} setup of the
+ Isabelle document preparation system would present
+ ``\verb,\,\verb,<alpha>,'' as @{text "\<alpha>"}, and
+ ``\verb,\,\verb,<^bold>,\verb,\,\verb,<alpha>,'' as @{text
+ "\<^bold>\<alpha>"}.
+*}
+
+text %mlref {*
+ \begin{mldecls}
+ @{index_ML_type "Symbol.symbol"} \\
+ @{index_ML Symbol.explode: "string -> Symbol.symbol list"} \\
+ @{index_ML Symbol.is_letter: "Symbol.symbol -> bool"} \\
+ @{index_ML Symbol.is_digit: "Symbol.symbol -> bool"} \\
+ @{index_ML Symbol.is_quasi: "Symbol.symbol -> bool"} \\
+ @{index_ML Symbol.is_blank: "Symbol.symbol -> bool"} \\
+ \end{mldecls}
+ \begin{mldecls}
+ @{index_ML_type "Symbol.sym"} \\
+ @{index_ML Symbol.decode: "Symbol.symbol -> Symbol.sym"} \\
+ \end{mldecls}
+
+ \begin{description}
+
+ \item @{ML_type "Symbol.symbol"} represents individual Isabelle
+ symbols; this is an alias for @{ML_type "string"}.
+
+ \item @{ML "Symbol.explode"}~@{text "str"} produces a symbol list
+ from the packed form. This function supercedes @{ML
+ "String.explode"} for virtually all purposes of manipulating text in
+ Isabelle!
+
+ \item @{ML "Symbol.is_letter"}, @{ML "Symbol.is_digit"}, @{ML
+ "Symbol.is_quasi"}, @{ML "Symbol.is_blank"} classify standard
+ symbols according to fixed syntactic conventions of Isabelle, cf.\
+ \cite{isabelle-isar-ref}.
+
+ \item @{ML_type "Symbol.sym"} is a concrete datatype that represents
+ the different kinds of symbols explicitly, with constructors @{ML
+ "Symbol.Char"}, @{ML "Symbol.Sym"}, @{ML "Symbol.Ctrl"}, @{ML
+ "Symbol.Raw"}.
+
+ \item @{ML "Symbol.decode"} converts the string representation of a
+ symbol into the datatype version.
+
+ \end{description}
+*}
+
+
+subsection {* Basic names \label{sec:basic-names} *}
+
+text {*
+ A \emph{basic name} essentially consists of a single Isabelle
+ identifier. There are conventions to mark separate classes of basic
+ names, by attaching a suffix of underscores (@{text "_"}): one
+ underscore means \emph{internal name}, two underscores means
+ \emph{Skolem name}, three underscores means \emph{internal Skolem
+ name}.
+
+ For example, the basic name @{text "foo"} has the internal version
+ @{text "foo_"}, with Skolem versions @{text "foo__"} and @{text
+ "foo___"}, respectively.
+
+ These special versions provide copies of the basic name space, apart
+ from anything that normally appears in the user text. For example,
+ system generated variables in Isar proof contexts are usually marked
+ as internal, which prevents mysterious name references like @{text
+ "xaa"} to appear in the text.
+
+ \medskip Manipulating binding scopes often requires on-the-fly
+ renamings. A \emph{name context} contains a collection of already
+ used names. The @{text "declare"} operation adds names to the
+ context.
+
+ The @{text "invents"} operation derives a number of fresh names from
+ a given starting point. For example, the first three names derived
+ from @{text "a"} are @{text "a"}, @{text "b"}, @{text "c"}.
+
+ The @{text "variants"} operation produces fresh names by
+ incrementing tentative names as base-26 numbers (with digits @{text
+ "a..z"}) until all clashes are resolved. For example, name @{text
+ "foo"} results in variants @{text "fooa"}, @{text "foob"}, @{text
+ "fooc"}, \dots, @{text "fooaa"}, @{text "fooab"} etc.; each renaming
+ step picks the next unused variant from this sequence.
+*}
+
+text %mlref {*
+ \begin{mldecls}
+ @{index_ML Name.internal: "string -> string"} \\
+ @{index_ML Name.skolem: "string -> string"} \\
+ \end{mldecls}
+ \begin{mldecls}
+ @{index_ML_type Name.context} \\
+ @{index_ML Name.context: Name.context} \\
+ @{index_ML Name.declare: "string -> Name.context -> Name.context"} \\
+ @{index_ML Name.invents: "Name.context -> string -> int -> string list"} \\
+ @{index_ML Name.variants: "string list -> Name.context -> string list * Name.context"} \\
+ \end{mldecls}
+
+ \begin{description}
+
+ \item @{ML Name.internal}~@{text "name"} produces an internal name
+ by adding one underscore.
+
+ \item @{ML Name.skolem}~@{text "name"} produces a Skolem name by
+ adding two underscores.
+
+ \item @{ML_type Name.context} represents the context of already used
+ names; the initial value is @{ML "Name.context"}.
+
+ \item @{ML Name.declare}~@{text "name"} enters a used name into the
+ context.
+
+ \item @{ML Name.invents}~@{text "context name n"} produces @{text
+ "n"} fresh names derived from @{text "name"}.
+
+ \item @{ML Name.variants}~@{text "names context"} produces fresh
+ varians of @{text "names"}; the result is entered into the context.
+
+ \end{description}
+*}
+
+
+subsection {* Indexed names *}
+
+text {*
+ An \emph{indexed name} (or @{text "indexname"}) is a pair of a basic
+ name and a natural number. This representation allows efficient
+ renaming by incrementing the second component only. The canonical
+ way to rename two collections of indexnames apart from each other is
+ this: determine the maximum index @{text "maxidx"} of the first
+ collection, then increment all indexes of the second collection by
+ @{text "maxidx + 1"}; the maximum index of an empty collection is
+ @{text "-1"}.
+
+ Occasionally, basic names and indexed names are injected into the
+ same pair type: the (improper) indexname @{text "(x, -1)"} is used
+ to encode basic names.
+
+ \medskip Isabelle syntax observes the following rules for
+ representing an indexname @{text "(x, i)"} as a packed string:
+
+ \begin{itemize}
+
+ \item @{text "?x"} if @{text "x"} does not end with a digit and @{text "i = 0"},
+
+ \item @{text "?xi"} if @{text "x"} does not end with a digit,
+
+ \item @{text "?x.i"} otherwise.
+
+ \end{itemize}
+
+ Indexnames may acquire large index numbers over time. Results are
+ normalized towards @{text "0"} at certain checkpoints, notably at
+ the end of a proof. This works by producing variants of the
+ corresponding basic name components. For example, the collection
+ @{text "?x1, ?x7, ?x42"} becomes @{text "?x, ?xa, ?xb"}.
+*}
+
+text %mlref {*
+ \begin{mldecls}
+ @{index_ML_type indexname} \\
+ \end{mldecls}
+
+ \begin{description}
+
+ \item @{ML_type indexname} represents indexed names. This is an
+ abbreviation for @{ML_type "string * int"}. The second component is
+ usually non-negative, except for situations where @{text "(x, -1)"}
+ is used to embed basic names into this type.
+
+ \end{description}
+*}
+
+
+subsection {* Qualified names and name spaces *}
+
+text {*
+ A \emph{qualified name} consists of a non-empty sequence of basic
+ name components. The packed representation uses a dot as separator,
+ as in ``@{text "A.b.c"}''. The last component is called \emph{base}
+ name, the remaining prefix \emph{qualifier} (which may be empty).
+ The idea of qualified names is to encode nested structures by
+ recording the access paths as qualifiers. For example, an item
+ named ``@{text "A.b.c"}'' may be understood as a local entity @{text
+ "c"}, within a local structure @{text "b"}, within a global
+ structure @{text "A"}. Typically, name space hierarchies consist of
+ 1--2 levels of qualification, but this need not be always so.
+
+ The empty name is commonly used as an indication of unnamed
+ entities, whenever this makes any sense. The basic operations on
+ qualified names are smart enough to pass through such improper names
+ unchanged.
+
+ \medskip A @{text "naming"} policy tells how to turn a name
+ specification into a fully qualified internal name (by the @{text
+ "full"} operation), and how fully qualified names may be accessed
+ externally. For example, the default naming policy is to prefix an
+ implicit path: @{text "full x"} produces @{text "path.x"}, and the
+ standard accesses for @{text "path.x"} include both @{text "x"} and
+ @{text "path.x"}. Normally, the naming is implicit in the theory or
+ proof context; there are separate versions of the corresponding.
+
+ \medskip A @{text "name space"} manages a collection of fully
+ internalized names, together with a mapping between external names
+ and internal names (in both directions). The corresponding @{text
+ "intern"} and @{text "extern"} operations are mostly used for
+ parsing and printing only! The @{text "declare"} operation augments
+ a name space according to the accesses determined by the naming
+ policy.
+
+ \medskip As a general principle, there is a separate name space for
+ each kind of formal entity, e.g.\ logical constant, type
+ constructor, type class, theorem. It is usually clear from the
+ occurrence in concrete syntax (or from the scope) which kind of
+ entity a name refers to. For example, the very same name @{text
+ "c"} may be used uniformly for a constant, type constructor, and
+ type class.
+
+ There are common schemes to name theorems systematically, according
+ to the name of the main logical entity involved, e.g.\ @{text
+ "c.intro"} for a canonical theorem related to constant @{text "c"}.
+ This technique of mapping names from one space into another requires
+ some care in order to avoid conflicts. In particular, theorem names
+ derived from a type constructor or type class are better suffixed in
+ addition to the usual qualification, e.g.\ @{text "c_type.intro"}
+ and @{text "c_class.intro"} for theorems related to type @{text "c"}
+ and class @{text "c"}, respectively.
+*}
+
+text %mlref {*
+ \begin{mldecls}
+ @{index_ML NameSpace.base: "string -> string"} \\
+ @{index_ML NameSpace.qualifier: "string -> string"} \\
+ @{index_ML NameSpace.append: "string -> string -> string"} \\
+ @{index_ML NameSpace.implode: "string list -> string"} \\
+ @{index_ML NameSpace.explode: "string -> string list"} \\
+ \end{mldecls}
+ \begin{mldecls}
+ @{index_ML_type NameSpace.naming} \\
+ @{index_ML NameSpace.default_naming: NameSpace.naming} \\
+ @{index_ML NameSpace.add_path: "string -> NameSpace.naming -> NameSpace.naming"} \\
+ @{index_ML NameSpace.full_name: "NameSpace.naming -> binding -> string"} \\
+ \end{mldecls}
+ \begin{mldecls}
+ @{index_ML_type NameSpace.T} \\
+ @{index_ML NameSpace.empty: NameSpace.T} \\
+ @{index_ML NameSpace.merge: "NameSpace.T * NameSpace.T -> NameSpace.T"} \\
+ @{index_ML NameSpace.declare: "NameSpace.naming -> binding -> NameSpace.T -> string * NameSpace.T"} \\
+ @{index_ML NameSpace.intern: "NameSpace.T -> string -> string"} \\
+ @{index_ML NameSpace.extern: "NameSpace.T -> string -> string"} \\
+ \end{mldecls}
+
+ \begin{description}
+
+ \item @{ML NameSpace.base}~@{text "name"} returns the base name of a
+ qualified name.
+
+ \item @{ML NameSpace.qualifier}~@{text "name"} returns the qualifier
+ of a qualified name.
+
+ \item @{ML NameSpace.append}~@{text "name\<^isub>1 name\<^isub>2"}
+ appends two qualified names.
+
+ \item @{ML NameSpace.implode}~@{text "name"} and @{ML
+ NameSpace.explode}~@{text "names"} convert between the packed string
+ representation and the explicit list form of qualified names.
+
+ \item @{ML_type NameSpace.naming} represents the abstract concept of
+ a naming policy.
+
+ \item @{ML NameSpace.default_naming} is the default naming policy.
+ In a theory context, this is usually augmented by a path prefix
+ consisting of the theory name.
+
+ \item @{ML NameSpace.add_path}~@{text "path naming"} augments the
+ naming policy by extending its path component.
+
+ \item @{ML NameSpace.full_name}@{text "naming binding"} turns a name
+ binding (usually a basic name) into the fully qualified
+ internal name, according to the given naming policy.
+
+ \item @{ML_type NameSpace.T} represents name spaces.
+
+ \item @{ML NameSpace.empty} and @{ML NameSpace.merge}~@{text
+ "(space\<^isub>1, space\<^isub>2)"} are the canonical operations for
+ maintaining name spaces according to theory data management
+ (\secref{sec:context-data}).
+
+ \item @{ML NameSpace.declare}~@{text "naming bindings space"} enters a
+ name binding as fully qualified internal name into the name space,
+ with external accesses determined by the naming policy.
+
+ \item @{ML NameSpace.intern}~@{text "space name"} internalizes a
+ (partially qualified) external name.
+
+ This operation is mostly for parsing! Note that fully qualified
+ names stemming from declarations are produced via @{ML
+ "NameSpace.full_name"} and @{ML "NameSpace.declare"}
+ (or their derivatives for @{ML_type theory} and
+ @{ML_type Proof.context}).
+
+ \item @{ML NameSpace.extern}~@{text "space name"} externalizes a
+ (fully qualified) internal name.
+
+ This operation is mostly for printing! Note unqualified names are
+ produced via @{ML NameSpace.base}.
+
+ \end{description}
+*}
+
+end