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doc-src/Locales/Locales/Examples3.thy

author | wenzelm |

Mon, 01 Mar 2010 21:41:35 +0100 | |

changeset 35423 | 6ef9525a5727 |

parent 33867 | 52643d0f856d |

child 37206 | 7f2a6f3143ad |

permissions | -rw-r--r-- |

eliminated hard tabs;

theory Examples3 imports Examples begin text {* \vspace{-5ex} *} subsection {* Third Version: Local Interpretation \label{sec:local-interpretation} *} text {* In the above example, the fact that @{term "op \<le>"} is a partial order for the integers was used in the second goal to discharge the premise in the definition of @{text "op \<sqsubset>"}. In general, proofs of the equations not only may involve definitions from the interpreted locale but arbitrarily complex arguments in the context of the locale. Therefore is would be convenient to have the interpreted locale conclusions temporary available in the proof. This can be achieved by a locale interpretation in the proof body. The command for local interpretations is \isakeyword{interpret}. We repeat the example from the previous section to illustrate this. *} interpretation %visible int: partial_order "op \<le> :: int \<Rightarrow> int \<Rightarrow> bool" where "partial_order.less op \<le> (x::int) y = (x < y)" proof - show "partial_order (op \<le> :: int \<Rightarrow> int \<Rightarrow> bool)" by unfold_locales auto then interpret int: partial_order "op \<le> :: [int, int] \<Rightarrow> bool" . show "partial_order.less op \<le> (x::int) y = (x < y)" unfolding int.less_def by auto qed text {* The inner interpretation is immediate from the preceding fact and proved by assumption (Isar short hand ``.''). It enriches the local proof context by the theorems also obtained in the interpretation from Section~\ref{sec:po-first}, and @{text int.less_def} may directly be used to unfold the definition. Theorems from the local interpretation disappear after leaving the proof context --- that is, after the succeeding \isakeyword{next} or \isakeyword{qed} statement. *} subsection {* Further Interpretations *} text {* Further interpretations are necessary for the other locales. In @{text lattice} the operations~@{text \<sqinter>} and~@{text \<squnion>} are substituted by @{term "min :: int \<Rightarrow> int \<Rightarrow> int"} and @{term "max :: int \<Rightarrow> int \<Rightarrow> int"}. The entire proof for the interpretation is reproduced to give an example of a more elaborate interpretation proof. Note that the equations are named so they can be used in a later example. *} interpretation %visible int: lattice "op \<le> :: int \<Rightarrow> int \<Rightarrow> bool" where int_min_eq: "lattice.meet op \<le> (x::int) y = min x y" and int_max_eq: "lattice.join op \<le> (x::int) y = max x y" proof - show "lattice (op \<le> :: int \<Rightarrow> int \<Rightarrow> bool)" txt {* \normalsize We have already shown that this is a partial order, *} apply unfold_locales txt {* \normalsize hence only the lattice axioms remain to be shown. @{subgoals [display]} By @{text is_inf} and @{text is_sup}, *} apply (unfold int.is_inf_def int.is_sup_def) txt {* \normalsize the goals are transformed to these statements: @{subgoals [display]} This is Presburger arithmetic, which can be solved by the method @{text arith}. *} by arith+ txt {* \normalsize In order to show the equations, we put ourselves in a situation where the lattice theorems can be used in a convenient way. *} then interpret int: lattice "op \<le> :: int \<Rightarrow> int \<Rightarrow> bool" . show "lattice.meet op \<le> (x::int) y = min x y" by (bestsimp simp: int.meet_def int.is_inf_def) show "lattice.join op \<le> (x::int) y = max x y" by (bestsimp simp: int.join_def int.is_sup_def) qed text {* Next follows that @{text "op \<le>"} is a total order, again for the integers. *} interpretation %visible int: total_order "op \<le> :: int \<Rightarrow> int \<Rightarrow> bool" by unfold_locales arith text {* Theorems that are available in the theory at this point are shown in Table~\ref{tab:int-lattice}. Two points are worth noting: \begin{table} \hrule \vspace{2ex} \begin{center} \begin{tabular}{l} @{thm [source] int.less_def} from locale @{text partial_order}: \\ \quad @{thm int.less_def} \\ @{thm [source] int.meet_left} from locale @{text lattice}: \\ \quad @{thm int.meet_left} \\ @{thm [source] int.join_distr} from locale @{text distrib_lattice}: \\ \quad @{thm int.join_distr} \\ @{thm [source] int.less_total} from locale @{text total_order}: \\ \quad @{thm int.less_total} \end{tabular} \end{center} \hrule \caption{Interpreted theorems for~@{text \<le>} on the integers.} \label{tab:int-lattice} \end{table} \begin{itemize} \item Locale @{text distrib_lattice} was also interpreted. Since the locale hierarchy reflects that total orders are distributive lattices, the interpretation of the latter was inserted automatically with the interpretation of the former. In general, interpretation traverses the locale hierarchy upwards and interprets all encountered locales, regardless whether imported or proved via the \isakeyword{sublocale} command. Existing interpretations are skipped avoiding duplicate work. \item The predicate @{term "op <"} appears in theorem @{thm [source] int.less_total} although an equation for the replacement of @{text "op \<sqsubset>"} was only given in the interpretation of @{text partial_order}. The interpretation equations are pushed downwards the hierarchy for related interpretations --- that is, for interpretations that share the instances of parameters they have in common. \end{itemize} *} text {* The interpretations for a locale $n$ within the current theory may be inspected with \isakeyword{print\_interps}~$n$. This prints the list of instances of $n$, for which interpretations exist. For example, \isakeyword{print\_interps} @{term partial_order} outputs the following: \begin{small} \begin{alltt} int! : partial_order "op \(\le\)" \end{alltt} \end{small} Of course, there is only one interpretation. The interpretation qualifier on the left is decorated with an exclamation point. This means that it is mandatory. Qualifiers can either be \emph{mandatory} or \emph{optional}, designated by ``!'' or ``?'' respectively. Mandatory qualifiers must occur in a name reference while optional ones need not. Mandatory qualifiers prevent accidental hiding of names, while optional qualifiers can be more convenient to use. For \isakeyword{interpretation}, the default is ``!''. *} section {* Locale Expressions \label{sec:expressions} *} text {* A map~@{term \<phi>} between partial orders~@{text \<sqsubseteq>} and~@{text \<preceq>} is called order preserving if @{text "x \<sqsubseteq> y"} implies @{text "\<phi> x \<preceq> \<phi> y"}. This situation is more complex than those encountered so far: it involves two partial orders, and it is desirable to use the existing locale for both. A locale for order preserving maps requires three parameters: @{text le}~(\isakeyword{infixl}~@{text \<sqsubseteq>}) and @{text le'}~(\isakeyword{infixl}~@{text \<preceq>}) for the orders and~@{text \<phi>} for the map. In order to reuse the existing locale for partial orders, which has the single parameter~@{text le}, it must be imported twice, once mapping its parameter to~@{text le} from the new locale and once to~@{text le'}. This can be achieved with a compound locale expression. In general, a locale expression is a sequence of \emph{locale instances} separated by~``$\textbf{+}$'' and followed by a \isakeyword{for} clause. An instance has the following format: \begin{quote} \textit{qualifier} \textbf{:} \textit{locale-name} \textit{parameter-instantiation} \end{quote} We have already seen locale instances as arguments to \isakeyword{interpretation} in Section~\ref{sec:interpretation}. As before, the qualifier serves to disambiguate names from different instances of the same locale. While in \isakeyword{interpretation} qualifiers default to mandatory, in import and in the \isakeyword{sublocale} command, they default to optional. Since the parameters~@{text le} and~@{text le'} are to be partial orders, our locale for order preserving maps will import the these instances: \begin{small} \begin{alltt} le: partial_order le le': partial_order le' \end{alltt} \end{small} For matter of convenience we choose to name parameter names and qualifiers alike. This is an arbitrary decision. Technically, qualifiers and parameters are unrelated. Having determined the instances, let us turn to the \isakeyword{for} clause. It serves to declare locale parameters in the same way as the context element \isakeyword{fixes} does. Context elements can only occur after the import section, and therefore the parameters referred to in the instances must be declared in the \isakeyword{for} clause. The \isakeyword{for} clause is also where the syntax of these parameters is declared. Two context elements for the map parameter~@{text \<phi>} and the assumptions that it is order preserving complete the locale declaration. *} locale order_preserving = le: partial_order le + le': partial_order le' for le (infixl "\<sqsubseteq>" 50) and le' (infixl "\<preceq>" 50) + fixes \<phi> assumes hom_le: "x \<sqsubseteq> y \<Longrightarrow> \<phi> x \<preceq> \<phi> y" text (in order_preserving) {* Here are examples of theorems that are available in the locale: \hspace*{1em}@{thm [source] hom_le}: @{thm hom_le} \hspace*{1em}@{thm [source] le.less_le_trans}: @{thm le.less_le_trans} \hspace*{1em}@{thm [source] le'.less_le_trans}: @{thm [display, indent=4] le'.less_le_trans} While there is infix syntax for the strict operation associated to @{term "op \<sqsubseteq>"}, there is none for the strict version of @{term "op \<preceq>"}. The abbreviation @{text less} with its infix syntax is only available for the original instance it was declared for. We may introduce the abbreviation @{text less'} with infix syntax~@{text \<prec>} with the following declaration: *} abbreviation (in order_preserving) less' (infixl "\<prec>" 50) where "less' \<equiv> partial_order.less le'" text (in order_preserving) {* Now the theorem is displayed nicely as @{thm [source] le'.less_le_trans}: @{thm [display, indent=2] le'.less_le_trans} *} text {* There are short notations for locale expressions. These are discussed in the following. *} subsection {* Default Instantiations *} text {* It is possible to omit parameter instantiations. The instantiation then defaults to the name of the parameter itself. For example, the locale expression @{text partial_order} is short for @{text "partial_order le"}, since the locale's single parameter is~@{text le}. We took advantage of this in the \isakeyword{sublocale} declarations of Section~\ref{sec:changing-the-hierarchy}. *} subsection {* Implicit Parameters \label{sec:implicit-parameters} *} text {* In a locale expression that occurs within a locale declaration, omitted parameters additionally extend the (possibly empty) \isakeyword{for} clause. The \isakeyword{for} clause is a general construct of Isabelle/Isar to mark names occurring in the preceding declaration as ``arbitrary but fixed''. This is necessary for example, if the name is already bound in a surrounding context. In a locale expression, names occurring in parameter instantiations should be bound by a \isakeyword{for} clause whenever these names are not introduced elsewhere in the context --- for example, on the left hand side of a \isakeyword{sublocale} declaration. There is an exception to this rule in locale declarations, where the \isakeyword{for} clause serves to declare locale parameters. Here, locale parameters for which no parameter instantiation is given are implicitly added, with their mixfix syntax, at the beginning of the \isakeyword{for} clause. For example, in a locale declaration, the expression @{text partial_order} is short for \begin{small} \begin{alltt} partial_order le \isakeyword{for} le (\isakeyword{infixl} "\(\sqsubseteq\)" 50)\textrm{.} \end{alltt} \end{small} This short hand was used in the locale declarations throughout Section~\ref{sec:import}. *} text{* The following locale declarations provide more examples. A map~@{text \<phi>} is a lattice homomorphism if it preserves meet and join. *} locale lattice_hom = le: lattice + le': lattice le' for le' (infixl "\<preceq>" 50) + fixes \<phi> assumes hom_meet: "\<phi> (x \<sqinter> y) = le'.meet (\<phi> x) (\<phi> y)" and hom_join: "\<phi> (x \<squnion> y) = le'.join (\<phi> x) (\<phi> y)" text {* The parameter instantiation in the first instance of @{term lattice} is omitted. This causes the parameter~@{text le} to be added to the \isakeyword{for} clause, and the locale has parameters~@{text le},~@{text le'} and, of course,~@{text \<phi>}. Before turning to the second example, we complete the locale by providing infix syntax for the meet and join operations of the second lattice. *} context lattice_hom begin abbreviation meet' (infixl "\<sqinter>''" 50) where "meet' \<equiv> le'.meet" abbreviation join' (infixl "\<squnion>''" 50) where "join' \<equiv> le'.join" end text {* The next example makes radical use of the short hand facilities. A homomorphism is an endomorphism if both orders coincide. *} locale lattice_end = lattice_hom _ le text {* The notation~@{text _} enables to omit a parameter in a positional instantiation. The omitted parameter,~@{text le} becomes the parameter of the declared locale and is, in the following position, used to instantiate the second parameter of @{text lattice_hom}. The effect is that of identifying the first in second parameter of the homomorphism locale. *} text {* The inheritance diagram of the situation we have now is shown in Figure~\ref{fig:hom}, where the dashed line depicts an interpretation which is introduced below. Parameter instantiations are indicated by $\sqsubseteq \mapsto \preceq$ etc. By looking at the inheritance diagram it would seem that two identical copies of each of the locales @{text partial_order} and @{text lattice} are imported by @{text lattice_end}. This is not the case! Inheritance paths with identical morphisms are automatically detected and the conclusions of the respective locales appear only once. \begin{figure} \hrule \vspace{2ex} \begin{center} \begin{tikzpicture} \node (o) at (0,0) {@{text partial_order}}; \node (oh) at (1.5,-2) {@{text order_preserving}}; \node (oh1) at (1.5,-0.7) {$\scriptscriptstyle \sqsubseteq \mapsto \sqsubseteq$}; \node (oh2) at (0,-1.3) {$\scriptscriptstyle \sqsubseteq \mapsto \preceq$}; \node (l) at (-1.5,-2) {@{text lattice}}; \node (lh) at (0,-4) {@{text lattice_hom}}; \node (lh1) at (0,-2.7) {$\scriptscriptstyle \sqsubseteq \mapsto \sqsubseteq$}; \node (lh2) at (-1.5,-3.3) {$\scriptscriptstyle \sqsubseteq \mapsto \preceq$}; \node (le) at (0,-6) {@{text lattice_end}}; \node (le1) at (0,-4.8) [anchor=west]{$\scriptscriptstyle \sqsubseteq \mapsto \sqsubseteq$}; \node (le2) at (0,-5.2) [anchor=west]{$\scriptscriptstyle \preceq \mapsto \sqsubseteq$}; \draw (o) -- (l); \draw[dashed] (oh) -- (lh); \draw (lh) -- (le); \draw (o) .. controls (oh1.south west) .. (oh); \draw (o) .. controls (oh2.north east) .. (oh); \draw (l) .. controls (lh1.south west) .. (lh); \draw (l) .. controls (lh2.north east) .. (lh); \end{tikzpicture} \end{center} \hrule \caption{Hierarchy of Homomorphism Locales.} \label{fig:hom} \end{figure} *} text {* It can be shown easily that a lattice homomorphism is order preserving. As the final example of this section, a locale interpretation is used to assert this: *} sublocale lattice_hom \<subseteq> order_preserving proof unfold_locales fix x y assume "x \<sqsubseteq> y" then have "y = (x \<squnion> y)" by (simp add: le.join_connection) then have "\<phi> y = (\<phi> x \<squnion>' \<phi> y)" by (simp add: hom_join [symmetric]) then show "\<phi> x \<preceq> \<phi> y" by (simp add: le'.join_connection) qed text (in lattice_hom) {* Theorems and other declarations --- syntax, in particular --- from the locale @{text order_preserving} are now active in @{text lattice_hom}, for example @{thm [source] hom_le}: @{thm [display, indent=2] hom_le} This theorem will be useful in the following section. *} section {* Conditional Interpretation *} text {* There are situations where an interpretation is not possible in the general case since the desired property is only valid if certain conditions are fulfilled. Take, for example, the function @{text "\<lambda>i. n * i"} that scales its argument by a constant factor. This function is order preserving (and even a lattice endomorphism) with respect to @{term "op \<le>"} provided @{text "n \<ge> 0"}. It is not possible to express this using a global interpretation, because it is in general unspecified whether~@{term n} is non-negative, but one may make an interpretation in an inner context of a proof where full information is available. This is not fully satisfactory either, since potentially interpretations may be required to make interpretations in many contexts. What is required is an interpretation that depends on the condition --- and this can be done with the \isakeyword{sublocale} command. For this purpose, we introduce a locale for the condition. *} locale non_negative = fixes n :: int assumes non_neg: "0 \<le> n" text {* It is again convenient to make the interpretation in an incremental fashion, first for order preserving maps, the for lattice endomorphisms. *} sublocale non_negative \<subseteq> order_preserving "op \<le>" "op \<le>" "\<lambda>i. n * i" using non_neg by unfold_locales (rule mult_left_mono) text {* While the proof of the previous interpretation is straightforward from monotonicity lemmas for~@{term "op *"}, the second proof follows a useful pattern. *} sublocale %visible non_negative \<subseteq> lattice_end "op \<le>" "\<lambda>i. n * i" proof (unfold_locales, unfold int_min_eq int_max_eq) txt {* \normalsize Unfolding the locale predicates \emph{and} the interpretation equations immediately yields two subgoals that reflect the core conjecture. @{subgoals [display]} It is now necessary to show, in the context of @{term non_negative}, that multiplication by~@{term n} commutes with @{term min} and @{term max}. *} qed (auto simp: hom_le) text (in order_preserving) {* The lemma @{thm [source] hom_le} simplifies a proof that would have otherwise been lengthy and we may consider making it a default rule for the simplifier: *} lemmas (in order_preserving) hom_le [simp] subsection {* Avoiding Infinite Chains of Interpretations \label{sec:infinite-chains} *} text {* Similar situations arise frequently in formalisations of abstract algebra where it is desirable to express that certain constructions preserve certain properties. For example, polynomials over rings are rings, or --- an example from the domain where the illustrations of this tutorial are taken from --- a partial order may be obtained for a function space by point-wise lifting of the partial order of the co-domain. This corresponds to the following interpretation: *} sublocale %visible partial_order \<subseteq> f: partial_order "\<lambda>f g. \<forall>x. f x \<sqsubseteq> g x" oops text {* Unfortunately this is a cyclic interpretation that leads to an infinite chain, namely @{text [display, indent=2] "partial_order \<subseteq> partial_order (\<lambda>f g. \<forall>x. f x \<sqsubseteq> g x) \<subseteq> partial_order (\<lambda>f g. \<forall>x y. f x y \<sqsubseteq> g x y) \<subseteq> \<dots>"} and the interpretation is rejected. Instead it is necessary to declare a locale that is logically equivalent to @{term partial_order} but serves to collect facts about functions spaces where the co-domain is a partial order, and to make the interpretation in its context: *} locale fun_partial_order = partial_order sublocale fun_partial_order \<subseteq> f: partial_order "\<lambda>f g. \<forall>x. f x \<sqsubseteq> g x" by unfold_locales (fast,rule,fast,blast intro: trans) text {* It is quite common in abstract algebra that such a construction maps a hierarchy of algebraic structures (or specifications) to a related hierarchy. By means of the same lifting, a function space is a lattice if its co-domain is a lattice: *} locale fun_lattice = fun_partial_order + lattice sublocale fun_lattice \<subseteq> f: lattice "\<lambda>f g. \<forall>x. f x \<sqsubseteq> g x" proof unfold_locales fix f g have "partial_order.is_inf (\<lambda>f g. \<forall>x. f x \<sqsubseteq> g x) f g (\<lambda>x. f x \<sqinter> g x)" apply (rule is_infI) apply rule+ apply (drule spec, assumption)+ done then show "\<exists>inf. partial_order.is_inf (\<lambda>f g. \<forall>x. f x \<sqsubseteq> g x) f g inf" by fast next fix f g have "partial_order.is_sup (\<lambda>f g. \<forall>x. f x \<sqsubseteq> g x) f g (\<lambda>x. f x \<squnion> g x)" apply (rule is_supI) apply rule+ apply (drule spec, assumption)+ done then show "\<exists>sup. partial_order.is_sup (\<lambda>f g. \<forall>x. f x \<sqsubseteq> g x) f g sup" by fast qed section {* Further Reading *} text {* More information on locales and their interpretation is available. For the locale hierarchy of import and interpretation dependencies see~\cite{Ballarin2006a}; interpretations in theories and proofs are covered in~\cite{Ballarin2006b}. In the latter, I show how interpretation in proofs enables to reason about families of algebraic structures, which cannot be expressed with locales directly. Haftmann and Wenzel~\cite{HaftmannWenzel2007} overcome a restriction of axiomatic type classes through a combination with locale interpretation. The result is a Haskell-style class system with a facility to generate ML and Haskell code. Classes are sufficient for simple specifications with a single type parameter. The locales for orders and lattices presented in this tutorial fall into this category. Order preserving maps, homomorphisms and vector spaces, on the other hand, do not. The locales reimplementation for Isabelle 2009 provides, among other improvements, a clean integration with Isabelle/Isar's local theory mechanisms, which are described in another paper by Haftmann and Wenzel~\cite{HaftmannWenzel2009}. The original work of Kamm\"uller on locales~\cite{KammullerEtAl1999} may be of interest from a historical perspective. My previous report on locales and locale expressions~\cite{Ballarin2004a} describes a simpler form of expressions than available now and is outdated. The mathematical background on orders and lattices is taken from Jacobson's textbook on algebra~\cite[Chapter~8]{Jacobson1985}. The sources of this tutorial, which include all proofs, are available with the Isabelle distribution at \url{http://isabelle.in.tum.de}. *} text {* \begin{table} \hrule \vspace{2ex} \begin{center} \begin{tabular}{l>$c<$l} \multicolumn{3}{l}{Miscellaneous} \\ \textit{attr-name} & ::= & \textit{name} $|$ \textit{attribute} $|$ \textit{name} \textit{attribute} \\ \textit{qualifier} & ::= & \textit{name} [``\textbf{?}'' $|$ ``\textbf{!}''] \\[2ex] \multicolumn{3}{l}{Context Elements} \\ \textit{fixes} & ::= & \textit{name} [ ``\textbf{::}'' \textit{type} ] [ ``\textbf{(}'' \textbf{structure} ``\textbf{)}'' $|$ \textit{mixfix} ] \\ \begin{comment} \textit{constrains} & ::= & \textit{name} ``\textbf{::}'' \textit{type} \\ \end{comment} \textit{assumes} & ::= & [ \textit{attr-name} ``\textbf{:}'' ] \textit{proposition} \\ \begin{comment} \textit{defines} & ::= & [ \textit{attr-name} ``\textbf{:}'' ] \textit{proposition} \\ \textit{notes} & ::= & [ \textit{attr-name} ``\textbf{=}'' ] ( \textit{qualified-name} [ \textit{attribute} ] )$^+$ \\ \end{comment} \textit{element} & ::= & \textbf{fixes} \textit{fixes} ( \textbf{and} \textit{fixes} )$^*$ \\ \begin{comment} & | & \textbf{constrains} \textit{constrains} ( \textbf{and} \textit{constrains} )$^*$ \\ \end{comment} & | & \textbf{assumes} \textit{assumes} ( \textbf{and} \textit{assumes} )$^*$ \\[2ex] %\begin{comment} % & | % & \textbf{defines} \textit{defines} ( \textbf{and} \textit{defines} )$^*$ \\ % & | % & \textbf{notes} \textit{notes} ( \textbf{and} \textit{notes} )$^*$ \\ %\end{comment} \multicolumn{3}{l}{Locale Expressions} \\ \textit{pos-insts} & ::= & ( \textit{term} $|$ ``\textbf{\_}'' )$^*$ \\ \textit{named-insts} & ::= & \textbf{where} \textit{name} ``\textbf{=}'' \textit{term} ( \textbf{and} \textit{name} ``\textbf{=}'' \textit{term} )$^*$ \\ \textit{instance} & ::= & [ \textit{qualifier} ``\textbf{:}'' ] \textit{name} ( \textit{pos-insts} $|$ \textit{named-inst} ) \\ \textit{expression} & ::= & \textit{instance} ( ``\textbf{+}'' \textit{instance} )$^*$ [ \textbf{for} \textit{fixes} ( \textbf{and} \textit{fixes} )$^*$ ] \\[2ex] \multicolumn{3}{l}{Declaration of Locales} \\ \textit{locale} & ::= & \textit{element}$^+$ \\ & | & \textit{expression} [ ``\textbf{+}'' \textit{element}$^+$ ] \\ \textit{toplevel} & ::= & \textbf{locale} \textit{name} [ ``\textbf{=}'' \textit{locale} ] \\[2ex] \multicolumn{3}{l}{Interpretation} \\ \textit{equation} & ::= & [ \textit{attr-name} ``\textbf{:}'' ] \textit{prop} \\ \textit{equations} & ::= & \textbf{where} \textit{equation} ( \textbf{and} \textit{equation} )$^*$ \\ \textit{toplevel} & ::= & \textbf{sublocale} \textit{name} ( ``$<$'' $|$ ``$\subseteq$'' ) \textit{expression} \textit{proof} \\ & | & \textbf{interpretation} \textit{expression} [ \textit{equations} ] \textit{proof} \\ & | & \textbf{interpret} \textit{expression} \textit{proof} \\[2ex] \multicolumn{3}{l}{Diagnostics} \\ \textit{toplevel} & ::= & \textbf{print\_locales} \\ & | & \textbf{print\_locale} [ ``\textbf{!}'' ] \textit{name} \\ & | & \textbf{print\_interps} \textit{name} \end{tabular} \end{center} \hrule \caption{Syntax of Locale Commands.} \label{tab:commands} \end{table} *} text {* \textbf{Revision History.} For the present third revision of the tutorial, much of the explanatory text was rewritten. Inheritance of interpretation equations is available with the forthcoming release of Isabelle, which at the time of editing these notes is expected for the end of 2009. The second revision accommodates changes introduced by the locales reimplementation for Isabelle 2009. Most notably locale expressions have been generalised from renaming to instantiation. *} text {* \textbf{Acknowledgements.} Alexander Krauss, Tobias Nipkow, Randy Pollack, Christian Sternagel and Makarius Wenzel have made useful comments on earlier versions of this document. The section on conditional interpretation was inspired by a number of e-mail enquiries the author received from locale users, and which suggested that this use case is important enough to deserve explicit explanation. The term \emph{conditional interpretation} is due to Larry Paulson. *} end