src/FOLP/hypsubst.ML
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     1 (*  Title: 	FOLP/hypsubst
       
     2     ID:         $Id$
       
     3     Author: 	Martin D Coen, Cambridge University Computer Laboratory
       
     4     Copyright   1995  University of Cambridge
       
     5 
       
     6 Original version of Provers/hypsubst.  Cannot use new version because it
       
     7 relies on the new simplifier!
       
     8 
       
     9 Martin Coen's tactic for substitution in the hypotheses
       
    10 *)
       
    11 
       
    12 signature HYPSUBST_DATA =
       
    13   sig
       
    14   val dest_eq	: term -> term*term
       
    15   val imp_intr	: thm		(* (P ==> Q) ==> P-->Q *)
       
    16   val rev_mp	: thm		(* [| P;  P-->Q |] ==> Q *)
       
    17   val subst	: thm		(* [| a=b;  P(a) |] ==> P(b) *)
       
    18   val sym	: thm		(* a=b ==> b=a *)
       
    19   end;
       
    20 
       
    21 signature HYPSUBST =
       
    22   sig
       
    23   val bound_hyp_subst_tac : int -> tactic
       
    24   val hyp_subst_tac       : int -> tactic
       
    25     (*exported purely for debugging purposes*)
       
    26   val eq_var              : bool -> term -> int * thm
       
    27   val inspect_pair        : bool -> term * term -> thm
       
    28   end;
       
    29 
       
    30 functor HypsubstFun(Data: HYPSUBST_DATA): HYPSUBST = 
       
    31 struct
       
    32 
       
    33 local open Data in
       
    34 
       
    35 exception EQ_VAR;
       
    36 
       
    37 fun loose (i,t) = 0 mem add_loose_bnos(t,i,[]);
       
    38 
       
    39 (*It's not safe to substitute for a constant; consider 0=1.
       
    40   It's not safe to substitute for x=t[x] since x is not eliminated.
       
    41   It's not safe to substitute for a Var; what if it appears in other goals?
       
    42   It's not safe to substitute for a variable free in the premises,
       
    43     but how could we check for this?*)
       
    44 fun inspect_pair bnd (t,u) =
       
    45   case (Pattern.eta_contract t, Pattern.eta_contract u) of
       
    46        (Bound i, _) => if loose(i,u) then raise Match 
       
    47 		       else sym		(*eliminates t*)
       
    48      | (_, Bound i) => if loose(i,t) then raise Match 
       
    49 		       else asm_rl	(*eliminates u*)
       
    50      | (Free _, _) => if bnd orelse Logic.occs(t,u) then raise Match 
       
    51 		      else sym		(*eliminates t*)
       
    52      | (_, Free _) => if bnd orelse Logic.occs(u,t) then raise Match 
       
    53 		      else asm_rl	(*eliminates u*)
       
    54      | _ => raise Match;
       
    55 
       
    56 (*Locates a substitutable variable on the left (resp. right) of an equality
       
    57    assumption.  Returns the number of intervening assumptions, paried with
       
    58    the rule asm_rl (resp. sym). *)
       
    59 fun eq_var bnd =
       
    60   let fun eq_var_aux k (Const("all",_) $ Abs(_,_,t)) = eq_var_aux k t
       
    61 	| eq_var_aux k (Const("==>",_) $ A $ B) = 
       
    62 	      ((k, inspect_pair bnd (dest_eq A))
       
    63 		      (*Exception Match comes from inspect_pair or dest_eq*)
       
    64 	       handle Match => eq_var_aux (k+1) B)
       
    65 	| eq_var_aux k _ = raise EQ_VAR
       
    66   in  eq_var_aux 0  end;
       
    67 
       
    68 (*Select a suitable equality assumption and substitute throughout the subgoal
       
    69   Replaces only Bound variables if bnd is true*)
       
    70 fun gen_hyp_subst_tac bnd i = DETERM (STATE(fn state =>
       
    71       let val (_,_,Bi,_) = dest_state(state,i)
       
    72 	  val n = length(Logic.strip_assums_hyp Bi) - 1
       
    73 	  val (k,symopt) = eq_var bnd Bi
       
    74       in 
       
    75 	 EVERY [REPEAT_DETERM_N k (etac rev_mp i),
       
    76 		etac revcut_rl i,
       
    77 		REPEAT_DETERM_N (n-k) (etac rev_mp i),
       
    78 		etac (symopt RS subst) i,
       
    79 		REPEAT_DETERM_N n (rtac imp_intr i)]
       
    80       end
       
    81       handle THM _ => no_tac | EQ_VAR => no_tac));
       
    82 
       
    83 (*Substitutes for Free or Bound variables*)
       
    84 val hyp_subst_tac = gen_hyp_subst_tac false;
       
    85 
       
    86 (*Substitutes for Bound variables only -- this is always safe*)
       
    87 val bound_hyp_subst_tac = gen_hyp_subst_tac true;
       
    88 
       
    89 end
       
    90 end;
       
    91