src/Pure/Isar/local_defs.ML
author wenzelm
Fri Apr 08 16:34:14 2011 +0200 (2011-04-08)
changeset 42290 b1f544c84040
parent 41228 e1fce873b814
child 42357 3305f573294e
permissions -rw-r--r--
discontinued special treatment of structure Lexicon;
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(*  Title:      Pure/Isar/local_defs.ML
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    Author:     Makarius
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Local definitions.
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*)
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signature LOCAL_DEFS =
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sig
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  val cert_def: Proof.context -> term -> (string * typ) * term
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  val abs_def: term -> (string * typ) * term
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  val mk_def: Proof.context -> (string * term) list -> term list
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  val expand: cterm list -> thm -> thm
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  val def_export: Assumption.export
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  val add_defs: ((binding * mixfix) * (Thm.binding * term)) list -> Proof.context ->
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    (term * (string * thm)) list * Proof.context
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  val add_def: (binding * mixfix) * term -> Proof.context -> (term * thm) * Proof.context
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  val fixed_abbrev: (binding * mixfix) * term -> Proof.context ->
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    (term * term) * Proof.context
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  val export: Proof.context -> Proof.context -> thm -> thm list * thm
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  val export_cterm: Proof.context -> Proof.context -> cterm -> thm list * cterm
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  val trans_terms: Proof.context -> thm list -> thm
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  val trans_props: Proof.context -> thm list -> thm
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  val contract: Proof.context -> thm list -> cterm -> thm -> thm
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  val print_rules: Proof.context -> unit
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  val defn_add: attribute
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  val defn_del: attribute
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  val meta_rewrite_conv: Proof.context -> conv
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  val meta_rewrite_rule: Proof.context -> thm -> thm
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  val unfold: Proof.context -> thm list -> thm -> thm
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  val unfold_goals: Proof.context -> thm list -> thm -> thm
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  val unfold_tac: Proof.context -> thm list -> tactic
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  val fold: Proof.context -> thm list -> thm -> thm
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  val fold_tac: Proof.context -> thm list -> tactic
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  val derived_def: Proof.context -> bool -> term ->
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    ((string * typ) * term) * (Proof.context -> thm -> thm)
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end;
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structure Local_Defs: LOCAL_DEFS =
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struct
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(** primitive definitions **)
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(* prepare defs *)
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fun cert_def ctxt eq =
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  let
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    fun err msg =
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      cat_error msg ("The error(s) above occurred in definition:\n" ^
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        quote (Syntax.string_of_term ctxt eq));
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    val ((lhs, _), eq') = eq
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      |> Sign.no_vars ctxt
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      |> Primitive_Defs.dest_def ctxt Term.is_Free (Variable.is_fixed ctxt) (K true)
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      handle TERM (msg, _) => err msg | ERROR msg => err msg;
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  in (Term.dest_Free (Term.head_of lhs), eq') end;
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val abs_def = Primitive_Defs.abs_def #>> Term.dest_Free;
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fun mk_def ctxt args =
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  let
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    val (xs, rhss) = split_list args;
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    val (bind, _) = ProofContext.bind_fixes xs ctxt;
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    val lhss = map (fn (x, rhs) => bind (Free (x, Term.fastype_of rhs))) args;
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  in map Logic.mk_equals (lhss ~~ rhss) end;
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(* export defs *)
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val head_of_def =
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  #1 o Term.dest_Free o Term.head_of o #1 o Logic.dest_equals o Term.strip_all_body;
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(*
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  [x, x == a]
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       :
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      B x
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  -----------
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      B a
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*)
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fun expand defs =
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  Drule.implies_intr_list defs
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  #> Drule.generalize ([], map (head_of_def o Thm.term_of) defs)
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  #> funpow (length defs) (fn th => Drule.reflexive_thm RS th);
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val expand_term = Envir.expand_term_frees o map (abs_def o Thm.term_of);
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fun def_export _ defs = (expand defs, expand_term defs);
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(* add defs *)
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fun add_defs defs ctxt =
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  let
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    val ((bvars, mxs), specs) = defs |> split_list |>> split_list;
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    val ((bfacts, atts), rhss) = specs |> split_list |>> split_list;
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    val xs = map Name.of_binding bvars;
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    val names = map2 Thm.def_binding_optional bvars bfacts;
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    val eqs = mk_def ctxt (xs ~~ rhss);
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    val lhss = map (fst o Logic.dest_equals) eqs;
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  in
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    ctxt
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    |> ProofContext.add_fixes (map2 (fn x => fn mx => (x, NONE, mx)) bvars mxs) |> #2
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    |> fold Variable.declare_term eqs
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    |> ProofContext.add_assms_i def_export
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      (map2 (fn a => fn eq => (a, [(eq, [])])) (names ~~ atts) eqs)
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    |>> map2 (fn lhs => fn (name, [th]) => (lhs, (name, th))) lhss
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  end;
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fun add_def (var, rhs) ctxt =
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  let val ([(lhs, (_, th))], ctxt') = add_defs [(var, (Thm.empty_binding, rhs))] ctxt
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  in ((lhs, th), ctxt') end;
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(* fixed_abbrev *)
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fun fixed_abbrev ((x, mx), rhs) ctxt =
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  let
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    val T = Term.fastype_of rhs;
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    val ([x'], ctxt') = ctxt
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      |> Variable.declare_term rhs
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      |> ProofContext.add_fixes [(x, SOME T, mx)];
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    val lhs = Free (x', T);
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    val _ = cert_def ctxt' (Logic.mk_equals (lhs, rhs));
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    fun abbrev_export _ _ = (I, Envir.expand_term_frees [((x', T), rhs)]);
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    val (_, ctxt'') = Assumption.add_assms abbrev_export [] ctxt';
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  in ((lhs, rhs), ctxt'') end;
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(* specific export -- result based on educated guessing *)
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(*
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  [xs, xs == as]
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        :
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       B xs
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  --------------
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       B as
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*)
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fun export inner outer =    (*beware of closure sizes*)
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  let
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    val exp = Assumption.export false inner outer;
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    val prems = Assumption.all_prems_of inner;
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  in fn th =>
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    let
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      val th' = exp th;
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      val still_fixed = map #1 (Thm.fold_terms Term.add_frees th' []);
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      val defs = prems |> filter_out (fn prem =>
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        (case try (head_of_def o Thm.prop_of) prem of
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          SOME x => member (op =) still_fixed x
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        | NONE => true));
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    in (map Drule.abs_def defs, th') end
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  end;
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(*
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  [xs, xs == as]
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        :
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     TERM b xs
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  --------------  and  --------------
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     TERM b as          b xs == b as
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*)
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fun export_cterm inner outer ct =
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  export inner outer (Drule.mk_term ct) ||> Drule.dest_term;
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(* basic transitivity reasoning -- modulo beta-eta *)
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local
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val is_trivial = Pattern.aeconv o Logic.dest_equals o Thm.prop_of;
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fun trans_list _ _ [] = raise Empty
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  | trans_list trans ctxt (th :: raw_eqs) =
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      (case filter_out is_trivial raw_eqs of
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        [] => th
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      | eqs =>
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          let val ((_, th' :: eqs'), ctxt') = Variable.import true (th :: eqs) ctxt
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          in singleton (Variable.export ctxt' ctxt) (fold trans eqs' th') end);
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in
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val trans_terms = trans_list (fn eq2 => fn eq1 => eq2 COMP (eq1 COMP Drule.transitive_thm));
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val trans_props = trans_list (fn eq => fn th => th COMP (eq COMP Drule.equal_elim_rule1));
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end;
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fun contract ctxt defs ct th =
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  trans_props ctxt [th, Thm.symmetric (Raw_Simplifier.rewrite true defs ct)];
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(** defived definitions **)
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(* transformation rules *)
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structure Rules = Generic_Data
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(
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  type T = thm list;
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  val empty = [];
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  val extend = I;
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  val merge = Thm.merge_thms;
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);
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fun print_rules ctxt =
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  Pretty.writeln (Pretty.big_list "definitional transformations:"
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    (map (Display.pretty_thm ctxt) (Rules.get (Context.Proof ctxt))));
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val defn_add = Thm.declaration_attribute (Rules.map o Thm.add_thm);
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val defn_del = Thm.declaration_attribute (Rules.map o Thm.del_thm);
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(* meta rewrite rules *)
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fun meta_rewrite_conv ctxt =
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  Raw_Simplifier.rewrite_cterm (false, false, false) (K (K NONE))
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    (Raw_Simplifier.context ctxt empty_ss
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      addeqcongs [Drule.equals_cong]    (*protect meta-level equality*)
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      addsimps (Rules.get (Context.Proof ctxt)));
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val meta_rewrite_rule = Conv.fconv_rule o meta_rewrite_conv;
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(* rewriting with object-level rules *)
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fun meta f ctxt = f o map (meta_rewrite_rule ctxt);
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val unfold       = meta Raw_Simplifier.rewrite_rule;
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val unfold_goals = meta Raw_Simplifier.rewrite_goals_rule;
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val unfold_tac   = meta Raw_Simplifier.rewrite_goals_tac;
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val fold         = meta Raw_Simplifier.fold_rule;
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val fold_tac     = meta Raw_Simplifier.fold_goals_tac;
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(* derived defs -- potentially within the object-logic *)
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fun derived_def ctxt conditional prop =
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  let
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    val ((c, T), rhs) = prop
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      |> Thm.cterm_of (ProofContext.theory_of ctxt)
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      |> meta_rewrite_conv ctxt
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      |> (snd o Logic.dest_equals o Thm.prop_of)
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      |> conditional ? Logic.strip_imp_concl
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      |> (abs_def o #2 o cert_def ctxt);
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    fun prove ctxt' def =
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      let
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        val frees = Term.fold_aterms (fn Free (x, _) =>
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          if Variable.is_fixed ctxt' x then I else insert (op =) x | _ => I) prop [];
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      in
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        Goal.prove ctxt' frees [] prop (K (ALLGOALS
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          (CONVERSION (meta_rewrite_conv ctxt') THEN'
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            rewrite_goal_tac [def] THEN'
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            resolve_tac [Drule.reflexive_thm])))
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        handle ERROR msg => cat_error msg "Failed to prove definitional specification"
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      end;
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  in (((c, T), rhs), prove) end;
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end;