TFL/rules.ML
author obua
Fri, 16 Sep 2005 21:02:15 +0200
changeset 17440 df77edc4f5d0
parent 17203 29b2563f5c11
child 17892 62c397c17d18
permissions -rw-r--r--
fixed HOL-light/Isabelle syntax incompatability via more protect_xxx functions

(*  Title:      TFL/rules.ML
    ID:         $Id$
    Author:     Konrad Slind, Cambridge University Computer Laboratory
    Copyright   1997  University of Cambridge

Emulation of HOL inference rules for TFL
*)

signature RULES =
sig
  val dest_thm : thm -> term list * term

  (* Inference rules *)
  val REFL      :cterm -> thm
  val ASSUME    :cterm -> thm
  val MP        :thm -> thm -> thm
  val MATCH_MP  :thm -> thm -> thm
  val CONJUNCT1 :thm -> thm
  val CONJUNCT2 :thm -> thm
  val CONJUNCTS :thm -> thm list
  val DISCH     :cterm -> thm -> thm
  val UNDISCH   :thm  -> thm
  val SPEC      :cterm -> thm -> thm
  val ISPEC     :cterm -> thm -> thm
  val ISPECL    :cterm list -> thm -> thm
  val GEN       :cterm -> thm -> thm
  val GENL      :cterm list -> thm -> thm
  val LIST_CONJ :thm list -> thm

  val SYM : thm -> thm
  val DISCH_ALL : thm -> thm
  val FILTER_DISCH_ALL : (term -> bool) -> thm -> thm
  val SPEC_ALL  : thm -> thm
  val GEN_ALL   : thm -> thm
  val IMP_TRANS : thm -> thm -> thm
  val PROVE_HYP : thm -> thm -> thm

  val CHOOSE : cterm * thm -> thm -> thm
  val EXISTS : cterm * cterm -> thm -> thm
  val EXISTL : cterm list -> thm -> thm
  val IT_EXISTS : (cterm*cterm) list -> thm -> thm

  val EVEN_ORS : thm list -> thm list
  val DISJ_CASESL : thm -> thm list -> thm

  val list_beta_conv : cterm -> cterm list -> thm
  val SUBS : thm list -> thm -> thm
  val simpl_conv : simpset -> thm list -> cterm -> thm

  val rbeta : thm -> thm
(* For debugging my isabelle solver in the conditional rewriter *)
  val term_ref : term list ref
  val thm_ref : thm list ref
  val ss_ref : simpset list ref
  val tracing : bool ref
  val CONTEXT_REWRITE_RULE : term * term list * thm * thm list
                             -> thm -> thm * term list
  val RIGHT_ASSOC : thm -> thm

  val prove : bool -> cterm * tactic -> thm
end;

structure Rules: RULES =
struct

structure S = USyntax;
structure U = Utils;
structure D = Dcterm;


fun RULES_ERR func mesg = U.ERR {module = "Rules", func = func, mesg = mesg};


fun cconcl thm = D.drop_prop (#prop (Thm.crep_thm thm));
fun chyps thm = map D.drop_prop (#hyps (Thm.crep_thm thm));

fun dest_thm thm =
  let val {prop,hyps,...} = Thm.rep_thm thm
  in (map HOLogic.dest_Trueprop hyps, HOLogic.dest_Trueprop prop) end
  handle TERM _ => raise RULES_ERR "dest_thm" "missing Trueprop";


(* Inference rules *)

(*---------------------------------------------------------------------------
 *        Equality (one step)
 *---------------------------------------------------------------------------*)

fun REFL tm = Thm.reflexive tm RS meta_eq_to_obj_eq
  handle THM (msg, _, _) => raise RULES_ERR "REFL" msg;

fun SYM thm = thm RS sym
  handle THM (msg, _, _) => raise RULES_ERR "SYM" msg;

fun ALPHA thm ctm1 =
  let
    val ctm2 = Thm.cprop_of thm;
    val ctm2_eq = Thm.reflexive ctm2;
    val ctm1_eq = Thm.reflexive ctm1;
  in Thm.equal_elim (Thm.transitive ctm2_eq ctm1_eq) thm end
  handle THM (msg, _, _) => raise RULES_ERR "ALPHA" msg;

fun rbeta th =
  (case D.strip_comb (cconcl th) of
    (_, [l, r]) => Thm.transitive th (Thm.beta_conversion false r)
  | _ => raise RULES_ERR "rbeta" "");


(*----------------------------------------------------------------------------
 *        Implication and the assumption list
 *
 * Assumptions get stuck on the meta-language assumption list. Implications
 * are in the object language, so discharging an assumption "A" from theorem
 * "B" results in something that looks like "A --> B".
 *---------------------------------------------------------------------------*)

fun ASSUME ctm = Thm.assume (D.mk_prop ctm);


(*---------------------------------------------------------------------------
 * Implication in TFL is -->. Meta-language implication (==>) is only used
 * in the implementation of some of the inference rules below.
 *---------------------------------------------------------------------------*)
fun MP th1 th2 = th2 RS (th1 RS mp)
  handle THM (msg, _, _) => raise RULES_ERR "MP" msg;

(*forces the first argument to be a proposition if necessary*)
fun DISCH tm thm = Thm.implies_intr (D.mk_prop tm) thm COMP impI
  handle THM (msg, _, _) => raise RULES_ERR "DISCH" msg;

fun DISCH_ALL thm = fold_rev DISCH (#hyps (Thm.crep_thm thm)) thm;


fun FILTER_DISCH_ALL P thm =
 let fun check tm = P (#t (Thm.rep_cterm tm))
 in  foldr (fn (tm,th) => if check tm then DISCH tm th else th)
              thm (chyps thm)
 end;

(* freezeT expensive! *)
fun UNDISCH thm =
   let val tm = D.mk_prop (#1 (D.dest_imp (cconcl (Thm.freezeT thm))))
   in Thm.implies_elim (thm RS mp) (ASSUME tm) end
   handle U.ERR _ => raise RULES_ERR "UNDISCH" ""
     | THM _ => raise RULES_ERR "UNDISCH" "";

fun PROVE_HYP ath bth = MP (DISCH (cconcl ath) bth) ath;

fun IMP_TRANS th1 th2 = th2 RS (th1 RS Thms.imp_trans)
  handle THM (msg, _, _) => raise RULES_ERR "IMP_TRANS" msg;


(*----------------------------------------------------------------------------
 *        Conjunction
 *---------------------------------------------------------------------------*)

fun CONJUNCT1 thm = thm RS conjunct1
  handle THM (msg, _, _) => raise RULES_ERR "CONJUNCT1" msg;

fun CONJUNCT2 thm = thm RS conjunct2
  handle THM (msg, _, _) => raise RULES_ERR "CONJUNCT2" msg;

fun CONJUNCTS th = CONJUNCTS (CONJUNCT1 th) @ CONJUNCTS (CONJUNCT2 th) handle U.ERR _ => [th];

fun LIST_CONJ [] = raise RULES_ERR "LIST_CONJ" "empty list"
  | LIST_CONJ [th] = th
  | LIST_CONJ (th :: rst) = MP (MP (conjI COMP (impI RS impI)) th) (LIST_CONJ rst)
      handle THM (msg, _, _) => raise RULES_ERR "LIST_CONJ" msg;


(*----------------------------------------------------------------------------
 *        Disjunction
 *---------------------------------------------------------------------------*)
local val {prop,sign,...} = rep_thm disjI1
      val [P,Q] = term_vars prop
      val disj1 = Thm.forall_intr (Thm.cterm_of sign Q) disjI1
in
fun DISJ1 thm tm = thm RS (forall_elim (D.drop_prop tm) disj1)
  handle THM (msg, _, _) => raise RULES_ERR "DISJ1" msg;
end;

local val {prop,sign,...} = rep_thm disjI2
      val [P,Q] = term_vars prop
      val disj2 = Thm.forall_intr (Thm.cterm_of sign P) disjI2
in
fun DISJ2 tm thm = thm RS (forall_elim (D.drop_prop tm) disj2)
  handle THM (msg, _, _) => raise RULES_ERR "DISJ2" msg;
end;


(*----------------------------------------------------------------------------
 *
 *                   A1 |- M1, ..., An |- Mn
 *     ---------------------------------------------------
 *     [A1 |- M1 \/ ... \/ Mn, ..., An |- M1 \/ ... \/ Mn]
 *
 *---------------------------------------------------------------------------*)


fun EVEN_ORS thms =
  let fun blue ldisjs [] _ = []
        | blue ldisjs (th::rst) rdisjs =
            let val tail = tl rdisjs
                val rdisj_tl = D.list_mk_disj tail
            in fold_rev DISJ2 ldisjs (DISJ1 th rdisj_tl)
               :: blue (ldisjs @ [cconcl th]) rst tail
            end handle U.ERR _ => [fold_rev DISJ2 ldisjs th]
   in blue [] thms (map cconcl thms) end;


(*----------------------------------------------------------------------------
 *
 *         A |- P \/ Q   B,P |- R    C,Q |- R
 *     ---------------------------------------------------
 *                     A U B U C |- R
 *
 *---------------------------------------------------------------------------*)

fun DISJ_CASES th1 th2 th3 =
  let
    val c = D.drop_prop (cconcl th1);
    val (disj1, disj2) = D.dest_disj c;
    val th2' = DISCH disj1 th2;
    val th3' = DISCH disj2 th3;
  in
    th3' RS (th2' RS (th1 RS Thms.tfl_disjE))
      handle THM (msg, _, _) => raise RULES_ERR "DISJ_CASES" msg
  end;


(*-----------------------------------------------------------------------------
 *
 *       |- A1 \/ ... \/ An     [A1 |- M, ..., An |- M]
 *     ---------------------------------------------------
 *                           |- M
 *
 * Note. The list of theorems may be all jumbled up, so we have to
 * first organize it to align with the first argument (the disjunctive
 * theorem).
 *---------------------------------------------------------------------------*)

fun organize eq =    (* a bit slow - analogous to insertion sort *)
 let fun extract a alist =
     let fun ex (_,[]) = raise RULES_ERR "organize" "not a permutation.1"
           | ex(left,h::t) = if (eq h a) then (h,rev left@t) else ex(h::left,t)
     in ex ([],alist)
     end
     fun place [] [] = []
       | place (a::rst) alist =
           let val (item,next) = extract a alist
           in item::place rst next
           end
       | place _ _ = raise RULES_ERR "organize" "not a permutation.2"
 in place
 end;
(* freezeT expensive! *)
fun DISJ_CASESL disjth thl =
   let val c = cconcl disjth
       fun eq th atm = exists (fn t => HOLogic.dest_Trueprop t
                                       aconv term_of atm)
                              (#hyps(rep_thm th))
       val tml = D.strip_disj c
       fun DL th [] = raise RULES_ERR "DISJ_CASESL" "no cases"
         | DL th [th1] = PROVE_HYP th th1
         | DL th [th1,th2] = DISJ_CASES th th1 th2
         | DL th (th1::rst) =
            let val tm = #2(D.dest_disj(D.drop_prop(cconcl th)))
             in DISJ_CASES th th1 (DL (ASSUME tm) rst) end
   in DL (freezeT disjth) (organize eq tml thl)
   end;


(*----------------------------------------------------------------------------
 *        Universals
 *---------------------------------------------------------------------------*)
local (* this is fragile *)
      val {prop,sign,...} = rep_thm spec
      val x = hd (tl (term_vars prop))
      val cTV = ctyp_of sign (type_of x)
      val gspec = forall_intr (cterm_of sign x) spec
in
fun SPEC tm thm =
   let val {sign,T,...} = rep_cterm tm
       val gspec' = instantiate ([(cTV, ctyp_of sign T)], []) gspec
   in
      thm RS (forall_elim tm gspec')
   end
end;

fun SPEC_ALL thm = fold SPEC (#1(D.strip_forall(cconcl thm))) thm;

val ISPEC = SPEC
val ISPECL = fold ISPEC;

(* Not optimized! Too complicated. *)
local val {prop,sign,...} = rep_thm allI
      val [P] = add_term_vars (prop, [])
      fun cty_theta s = map (fn (i, (S, ty)) => (ctyp_of s (TVar (i, S)), ctyp_of s ty))
      fun ctm_theta s = map (fn (i, (_, tm2)) =>
                             let val ctm2 = cterm_of s tm2
                             in (cterm_of s (Var(i,#T(rep_cterm ctm2))), ctm2)
                             end)
      fun certify s (ty_theta,tm_theta) =
        (cty_theta s (Vartab.dest ty_theta),
         ctm_theta s (Vartab.dest tm_theta))
in
fun GEN v th =
   let val gth = forall_intr v th
       val {prop=Const("all",_)$Abs(x,ty,rst),sign,...} = rep_thm gth
       val P' = Abs(x,ty, HOLogic.dest_Trueprop rst)  (* get rid of trueprop *)
       val theta = Pattern.match sign (P,P')
       val allI2 = instantiate (certify sign theta) allI
       val thm = Thm.implies_elim allI2 gth
       val {prop = tp $ (A $ Abs(_,_,M)),sign,...} = rep_thm thm
       val prop' = tp $ (A $ Abs(x,ty,M))
   in ALPHA thm (cterm_of sign prop')
   end
end;

val GENL = fold_rev GEN;

fun GEN_ALL thm =
   let val {prop,sign,...} = rep_thm thm
       val tycheck = cterm_of sign
       val vlist = map tycheck (add_term_vars (prop, []))
  in GENL vlist thm
  end;


fun MATCH_MP th1 th2 =
   if (D.is_forall (D.drop_prop(cconcl th1)))
   then MATCH_MP (th1 RS spec) th2
   else MP th1 th2;


(*----------------------------------------------------------------------------
 *        Existentials
 *---------------------------------------------------------------------------*)



(*---------------------------------------------------------------------------
 * Existential elimination
 *
 *      A1 |- ?x.t[x]   ,   A2, "t[v]" |- t'
 *      ------------------------------------     (variable v occurs nowhere)
 *                A1 u A2 |- t'
 *
 *---------------------------------------------------------------------------*)

fun CHOOSE (fvar, exth) fact =
  let
    val lam = #2 (D.dest_comb (D.drop_prop (cconcl exth)))
    val redex = D.capply lam fvar
    val {sign, t = t$u,...} = Thm.rep_cterm redex
    val residue = Thm.cterm_of sign (betapply (t, u))
  in
    GEN fvar (DISCH residue fact) RS (exth RS Thms.choose_thm)
      handle THM (msg, _, _) => raise RULES_ERR "CHOOSE" msg
  end;

local val {prop,sign,...} = rep_thm exI
      val [P,x] = term_vars prop
in
fun EXISTS (template,witness) thm =
   let val {prop,sign,...} = rep_thm thm
       val P' = cterm_of sign P
       val x' = cterm_of sign x
       val abstr = #2 (D.dest_comb template)
   in
   thm RS (cterm_instantiate[(P',abstr), (x',witness)] exI)
     handle THM (msg, _, _) => raise RULES_ERR "EXISTS" msg
   end
end;

(*----------------------------------------------------------------------------
 *
 *         A |- M
 *   -------------------   [v_1,...,v_n]
 *    A |- ?v1...v_n. M
 *
 *---------------------------------------------------------------------------*)

fun EXISTL vlist th =
  fold_rev (fn v => fn thm => EXISTS(D.mk_exists(v,cconcl thm), v) thm)
           vlist th;


(*----------------------------------------------------------------------------
 *
 *       A |- M[x_1,...,x_n]
 *   ----------------------------   [(x |-> y)_1,...,(x |-> y)_n]
 *       A |- ?y_1...y_n. M
 *
 *---------------------------------------------------------------------------*)
(* Could be improved, but needs "subst_free" for certified terms *)

fun IT_EXISTS blist th =
   let val {sign,...} = rep_thm th
       val tych = cterm_of sign
       val detype = #t o rep_cterm
       val blist' = map (fn (x,y) => (detype x, detype y)) blist
       fun ex v M  = cterm_of sign (S.mk_exists{Bvar=v,Body = M})

  in
  fold_rev (fn (b as (r1,r2)) => fn thm =>
        EXISTS(ex r2 (subst_free [b]
                   (HOLogic.dest_Trueprop(#prop(rep_thm thm)))), tych r1)
              thm)
       blist' th
  end;

(*---------------------------------------------------------------------------
 *  Faster version, that fails for some as yet unknown reason
 * fun IT_EXISTS blist th =
 *    let val {sign,...} = rep_thm th
 *        val tych = cterm_of sign
 *        fun detype (x,y) = ((#t o rep_cterm) x, (#t o rep_cterm) y)
 *   in
 *  fold (fn (b as (r1,r2), thm) =>
 *  EXISTS(D.mk_exists(r2, tych(subst_free[detype b](#t(rep_cterm(cconcl thm))))),
 *           r1) thm)  blist th
 *   end;
 *---------------------------------------------------------------------------*)

(*----------------------------------------------------------------------------
 *        Rewriting
 *---------------------------------------------------------------------------*)

fun SUBS thl =
  rewrite_rule (map (fn th => th RS eq_reflection handle THM _ => th) thl);

val rew_conv = MetaSimplifier.rewrite_cterm (true, false, false) (K (K NONE));

fun simpl_conv ss thl ctm =
 rew_conv (ss addsimps thl) ctm RS meta_eq_to_obj_eq;


val RIGHT_ASSOC = rewrite_rule [Thms.disj_assoc];



(*---------------------------------------------------------------------------
 *                  TERMINATION CONDITION EXTRACTION
 *---------------------------------------------------------------------------*)


(* Object language quantifier, i.e., "!" *)
fun Forall v M = S.mk_forall{Bvar=v, Body=M};


(* Fragile: it's a cong if it is not "R y x ==> cut f R x y = f y" *)
fun is_cong thm =
  let val {prop, ...} = rep_thm thm
  in case prop
     of (Const("==>",_)$(Const("Trueprop",_)$ _) $
         (Const("==",_) $ (Const ("Wellfounded_Recursion.cut",_) $ f $ R $ a $ x) $ _)) => false
      | _ => true
  end;



fun dest_equal(Const ("==",_) $
               (Const ("Trueprop",_) $ lhs)
               $ (Const ("Trueprop",_) $ rhs)) = {lhs=lhs, rhs=rhs}
  | dest_equal(Const ("==",_) $ lhs $ rhs)  = {lhs=lhs, rhs=rhs}
  | dest_equal tm = S.dest_eq tm;

fun get_lhs tm = #lhs(dest_equal (HOLogic.dest_Trueprop tm));

fun dest_all used (Const("all",_) $ (a as Abs _)) = S.dest_abs used a
  | dest_all _ _ = raise RULES_ERR "dest_all" "not a !!";

val is_all = can (dest_all []);

fun strip_all used fm =
   if (is_all fm)
   then let val ({Bvar, Body}, used') = dest_all used fm
            val (bvs, core, used'') = strip_all used' Body
        in ((Bvar::bvs), core, used'')
        end
   else ([], fm, used);

fun break_all(Const("all",_) $ Abs (_,_,body)) = body
  | break_all _ = raise RULES_ERR "break_all" "not a !!";

fun list_break_all(Const("all",_) $ Abs (s,ty,body)) =
     let val (L,core) = list_break_all body
     in ((s,ty)::L, core)
     end
  | list_break_all tm = ([],tm);

(*---------------------------------------------------------------------------
 * Rename a term of the form
 *
 *      !!x1 ...xn. x1=M1 ==> ... ==> xn=Mn
 *                  ==> ((%v1...vn. Q) x1 ... xn = g x1 ... xn.
 * to one of
 *
 *      !!v1 ... vn. v1=M1 ==> ... ==> vn=Mn
 *      ==> ((%v1...vn. Q) v1 ... vn = g v1 ... vn.
 *
 * This prevents name problems in extraction, and helps the result to read
 * better. There is a problem with varstructs, since they can introduce more
 * than n variables, and some extra reasoning needs to be done.
 *---------------------------------------------------------------------------*)

fun get ([],_,L) = rev L
  | get (ant::rst,n,L) =
      case (list_break_all ant)
        of ([],_) => get (rst, n+1,L)
         | (vlist,body) =>
            let val eq = Logic.strip_imp_concl body
                val (f,args) = S.strip_comb (get_lhs eq)
                val (vstrl,_) = S.strip_abs f
                val names  = variantlist (map (#1 o dest_Free) vstrl,
                                          add_term_names(body, []))
            in get (rst, n+1, (names,n)::L) end
            handle TERM _ => get (rst, n+1, L)
              | U.ERR _ => get (rst, n+1, L);

(* Note: rename_params_rule counts from 1, not 0 *)
fun rename thm =
  let val {prop,sign,...} = rep_thm thm
      val tych = cterm_of sign
      val ants = Logic.strip_imp_prems prop
      val news = get (ants,1,[])
  in
  fold rename_params_rule news thm
  end;


(*---------------------------------------------------------------------------
 * Beta-conversion to the rhs of an equation (taken from hol90/drule.sml)
 *---------------------------------------------------------------------------*)

fun list_beta_conv tm =
  let fun rbeta th = Thm.transitive th (beta_conversion false (#2(D.dest_eq(cconcl th))))
      fun iter [] = Thm.reflexive tm
        | iter (v::rst) = rbeta (combination(iter rst) (Thm.reflexive v))
  in iter  end;


(*---------------------------------------------------------------------------
 * Trace information for the rewriter
 *---------------------------------------------------------------------------*)
val term_ref = ref[] : term list ref
val ss_ref = ref [] : simpset list ref;
val thm_ref = ref [] : thm list ref;
val tracing = ref false;

fun say s = if !tracing then writeln s else ();

fun print_thms s L =
  say (cat_lines (s :: map string_of_thm L));

fun print_cterms s L =
  say (cat_lines (s :: map string_of_cterm L));


(*---------------------------------------------------------------------------
 * General abstraction handlers, should probably go in USyntax.
 *---------------------------------------------------------------------------*)
fun mk_aabs (vstr, body) =
  S.mk_abs {Bvar = vstr, Body = body}
  handle U.ERR _ => S.mk_pabs {varstruct = vstr, body = body};

fun list_mk_aabs (vstrl,tm) =
    fold_rev (fn vstr => fn tm => mk_aabs(vstr,tm)) vstrl tm;

fun dest_aabs used tm =
   let val ({Bvar,Body}, used') = S.dest_abs used tm
   in (Bvar, Body, used') end
   handle U.ERR _ =>
     let val {varstruct, body, used} = S.dest_pabs used tm
     in (varstruct, body, used) end;

fun strip_aabs used tm =
   let val (vstr, body, used') = dest_aabs used tm
       val (bvs, core, used'') = strip_aabs used' body
   in (vstr::bvs, core, used'') end
   handle U.ERR _ => ([], tm, used);

fun dest_combn tm 0 = (tm,[])
  | dest_combn tm n =
     let val {Rator,Rand} = S.dest_comb tm
         val (f,rands) = dest_combn Rator (n-1)
     in (f,Rand::rands)
     end;




local fun dest_pair M = let val {fst,snd} = S.dest_pair M in (fst,snd) end
      fun mk_fst tm =
          let val ty as Type("*", [fty,sty]) = type_of tm
          in  Const ("fst", ty --> fty) $ tm  end
      fun mk_snd tm =
          let val ty as Type("*", [fty,sty]) = type_of tm
          in  Const ("snd", ty --> sty) $ tm  end
in
fun XFILL tych x vstruct =
  let fun traverse p xocc L =
        if (is_Free p)
        then tych xocc::L
        else let val (p1,p2) = dest_pair p
             in traverse p1 (mk_fst xocc) (traverse p2  (mk_snd xocc) L)
             end
  in
  traverse vstruct x []
end end;

(*---------------------------------------------------------------------------
 * Replace a free tuple (vstr) by a universally quantified variable (a).
 * Note that the notion of "freeness" for a tuple is different than for a
 * variable: if variables in the tuple also occur in any other place than
 * an occurrences of the tuple, they aren't "free" (which is thus probably
 *  the wrong word to use).
 *---------------------------------------------------------------------------*)

fun VSTRUCT_ELIM tych a vstr th =
  let val L = S.free_vars_lr vstr
      val bind1 = tych (HOLogic.mk_Trueprop (HOLogic.mk_eq(a,vstr)))
      val thm1 = implies_intr bind1 (SUBS [SYM(assume bind1)] th)
      val thm2 = forall_intr_list (map tych L) thm1
      val thm3 = forall_elim_list (XFILL tych a vstr) thm2
  in refl RS
     rewrite_rule [Thm.symmetric (surjective_pairing RS eq_reflection)] thm3
  end;

fun PGEN tych a vstr th =
  let val a1 = tych a
      val vstr1 = tych vstr
  in
  forall_intr a1
     (if (is_Free vstr)
      then cterm_instantiate [(vstr1,a1)] th
      else VSTRUCT_ELIM tych a vstr th)
  end;


(*---------------------------------------------------------------------------
 * Takes apart a paired beta-redex, looking like "(\(x,y).N) vstr", into
 *
 *     (([x,y],N),vstr)
 *---------------------------------------------------------------------------*)
fun dest_pbeta_redex used M n =
  let val (f,args) = dest_combn M n
      val dummy = dest_aabs used f
  in (strip_aabs used f,args)
  end;

fun pbeta_redex M n = can (U.C (dest_pbeta_redex []) n) M;

fun dest_impl tm =
  let val ants = Logic.strip_imp_prems tm
      val eq = Logic.strip_imp_concl tm
  in (ants,get_lhs eq)
  end;

fun restricted t = isSome (S.find_term
                            (fn (Const("Wellfounded_Recursion.cut",_)) =>true | _ => false)
                            t)

fun CONTEXT_REWRITE_RULE (func, G, cut_lemma, congs) th =
 let val globals = func::G
     val pbeta_reduce = simpl_conv empty_ss [split_conv RS eq_reflection];
     val tc_list = ref[]: term list ref
     val dummy = term_ref := []
     val dummy = thm_ref  := []
     val dummy = ss_ref  := []
     val cut_lemma' = cut_lemma RS eq_reflection
     fun prover used ss thm =
     let fun cong_prover ss thm =
         let val dummy = say "cong_prover:"
             val cntxt = MetaSimplifier.prems_of_ss ss
             val dummy = print_thms "cntxt:" cntxt
             val dummy = say "cong rule:"
             val dummy = say (string_of_thm thm)
             val dummy = thm_ref := (thm :: !thm_ref)
             val dummy = ss_ref := (ss :: !ss_ref)
             (* Unquantified eliminate *)
             fun uq_eliminate (thm,imp,sign) =
                 let val tych = cterm_of sign
                     val dummy = print_cterms "To eliminate:" [tych imp]
                     val ants = map tych (Logic.strip_imp_prems imp)
                     val eq = Logic.strip_imp_concl imp
                     val lhs = tych(get_lhs eq)
                     val ss' = MetaSimplifier.add_prems (map ASSUME ants) ss
                     val lhs_eq_lhs1 = MetaSimplifier.rewrite_cterm (false,true,false) (prover used) ss' lhs
                       handle U.ERR _ => Thm.reflexive lhs
                     val dummy = print_thms "proven:" [lhs_eq_lhs1]
                     val lhs_eq_lhs2 = implies_intr_list ants lhs_eq_lhs1
                     val lhs_eeq_lhs2 = lhs_eq_lhs2 RS meta_eq_to_obj_eq
                  in
                  lhs_eeq_lhs2 COMP thm
                  end
             fun pq_eliminate (thm,sign,vlist,imp_body,lhs_eq) =
              let val ((vstrl, _, used'), args) = dest_pbeta_redex used lhs_eq (length vlist)
                  val dummy = assert (forall (op aconv)
                                      (ListPair.zip (vlist, args)))
                               "assertion failed in CONTEXT_REWRITE_RULE"
                  val imp_body1 = subst_free (ListPair.zip (args, vstrl))
                                             imp_body
                  val tych = cterm_of sign
                  val ants1 = map tych (Logic.strip_imp_prems imp_body1)
                  val eq1 = Logic.strip_imp_concl imp_body1
                  val Q = get_lhs eq1
                  val QeqQ1 = pbeta_reduce (tych Q)
                  val Q1 = #2(D.dest_eq(cconcl QeqQ1))
                  val ss' = MetaSimplifier.add_prems (map ASSUME ants1) ss
                  val Q1eeqQ2 = MetaSimplifier.rewrite_cterm (false,true,false) (prover used') ss' Q1
                                handle U.ERR _ => Thm.reflexive Q1
                  val Q2 = #2 (Logic.dest_equals (Thm.prop_of Q1eeqQ2))
                  val Q3 = tych(list_comb(list_mk_aabs(vstrl,Q2),vstrl))
                  val Q2eeqQ3 = Thm.symmetric(pbeta_reduce Q3 RS eq_reflection)
                  val thA = Thm.transitive(QeqQ1 RS eq_reflection) Q1eeqQ2
                  val QeeqQ3 = Thm.transitive thA Q2eeqQ3 handle THM _ =>
                               ((Q2eeqQ3 RS meta_eq_to_obj_eq)
                                RS ((thA RS meta_eq_to_obj_eq) RS trans))
                                RS eq_reflection
                  val impth = implies_intr_list ants1 QeeqQ3
                  val impth1 = impth RS meta_eq_to_obj_eq
                  (* Need to abstract *)
                  val ant_th = U.itlist2 (PGEN tych) args vstrl impth1
              in ant_th COMP thm
              end
             fun q_eliminate (thm,imp,sign) =
              let val (vlist, imp_body, used') = strip_all used imp
                  val (ants,Q) = dest_impl imp_body
              in if (pbeta_redex Q) (length vlist)
                 then pq_eliminate (thm,sign,vlist,imp_body,Q)
                 else
                 let val tych = cterm_of sign
                     val ants1 = map tych ants
                     val ss' = MetaSimplifier.add_prems (map ASSUME ants1) ss
                     val Q_eeq_Q1 = MetaSimplifier.rewrite_cterm
                        (false,true,false) (prover used') ss' (tych Q)
                      handle U.ERR _ => Thm.reflexive (tych Q)
                     val lhs_eeq_lhs2 = implies_intr_list ants1 Q_eeq_Q1
                     val lhs_eq_lhs2 = lhs_eeq_lhs2 RS meta_eq_to_obj_eq
                     val ant_th = forall_intr_list(map tych vlist)lhs_eq_lhs2
                 in
                 ant_th COMP thm
              end end

             fun eliminate thm =
               case (rep_thm thm)
               of {prop = (Const("==>",_) $ imp $ _), sign, ...} =>
                   eliminate
                    (if not(is_all imp)
                     then uq_eliminate (thm,imp,sign)
                     else q_eliminate (thm,imp,sign))
                            (* Assume that the leading constant is ==,   *)
                | _ => thm  (* if it is not a ==>                        *)
         in SOME(eliminate (rename thm)) end
         handle U.ERR _ => NONE    (* FIXME handle THM as well?? *)

        fun restrict_prover ss thm =
          let val dummy = say "restrict_prover:"
              val cntxt = rev(MetaSimplifier.prems_of_ss ss)
              val dummy = print_thms "cntxt:" cntxt
              val {prop = Const("==>",_) $ (Const("Trueprop",_) $ A) $ _,
                   sign,...} = rep_thm thm
              fun genl tm = let val vlist = gen_rems (op aconv)
                                           (add_term_frees(tm,[]), globals)
                            in fold_rev Forall vlist tm
                            end
              (*--------------------------------------------------------------
               * This actually isn't quite right, since it will think that
               * not-fully applied occs. of "f" in the context mean that the
               * current call is nested. The real solution is to pass in a
               * term "f v1..vn" which is a pattern that any full application
               * of "f" will match.
               *-------------------------------------------------------------*)
              val func_name = #1(dest_Const func)
              fun is_func (Const (name,_)) = (name = func_name)
                | is_func _                = false
              val rcontext = rev cntxt
              val cncl = HOLogic.dest_Trueprop o Thm.prop_of
              val antl = case rcontext of [] => []
                         | _   => [S.list_mk_conj(map cncl rcontext)]
              val TC = genl(S.list_mk_imp(antl, A))
              val dummy = print_cterms "func:" [cterm_of sign func]
              val dummy = print_cterms "TC:"
                              [cterm_of sign (HOLogic.mk_Trueprop TC)]
              val dummy = tc_list := (TC :: !tc_list)
              val nestedp = isSome (S.find_term is_func TC)
              val dummy = if nestedp then say "nested" else say "not_nested"
              val dummy = term_ref := ([func,TC]@(!term_ref))
              val th' = if nestedp then raise RULES_ERR "solver" "nested function"
                        else let val cTC = cterm_of sign
                                              (HOLogic.mk_Trueprop TC)
                             in case rcontext of
                                [] => SPEC_ALL(ASSUME cTC)
                               | _ => MP (SPEC_ALL (ASSUME cTC))
                                         (LIST_CONJ rcontext)
                             end
              val th'' = th' RS thm
          in SOME (th'')
          end handle U.ERR _ => NONE    (* FIXME handle THM as well?? *)
    in
    (if (is_cong thm) then cong_prover else restrict_prover) ss thm
    end
    val ctm = cprop_of th
    val names = add_term_names (term_of ctm, [])
    val th1 = MetaSimplifier.rewrite_cterm(false,true,false)
      (prover names) (empty_ss addsimps [cut_lemma'] addeqcongs congs) ctm
    val th2 = equal_elim th1 th
 in
 (th2, List.filter (not o restricted) (!tc_list))
 end;


fun prove strict (ptm, tac) =
  let val result =
    if strict then Goals.prove_goalw_cterm [] ptm (fn _ => [tac])
    else
      transform_error (fn () =>
        Goals.prove_goalw_cterm [] ptm (fn _ => [tac])) ()
      handle ERROR_MESSAGE msg => (warning msg; raise RULES_ERR "prove" msg);
  in #1 (freeze_thaw result) end;


end;