src/Provers/hypsubst.ML

 Martin Coen's tactic for substitution in the hypotheses
 *)
 
 signature HYPSUBST_DATA =
   sig
-  val dest_eq: term -> term*term
-  val imp_intr: thm	(* (P ==> Q) ==> P-->Q *)
-  val rev_cut_eq: thm	(* [| a=b;  a=b ==> R |] ==> R *)
-  val rev_mp: thm	(* [| P;  P-->Q |] ==> Q *)
-  val subst: thm	(* [| a=b;  P(a) |] ==> P(b) *)
-  val sym: thm		(* a=b ==> b=a *)
+  val dest_eq	: term -> term*term
+  val imp_intr	: thm		(* (P ==> Q) ==> P-->Q *)
+  val rev_mp	: thm		(* [| P;  P-->Q |] ==> Q *)
+  val subst	: thm		(* [| a=b;  P(a) |] ==> P(b) *)
+  val sym	: thm		(* a=b ==> b=a *)
   end;
 
 signature HYPSUBST =
   sig
   val bound_hyp_subst_tac : int -> tactic
   val hyp_subst_tac       : int -> tactic
     (*exported purely for debugging purposes*)
-  val eq_var              : bool -> term -> term * thm
-  val inspect_pair        : bool -> term * term -> term * thm
-  val liftvar             : int -> typ list -> term
+  val eq_var              : bool -> term -> int * thm
+  val inspect_pair        : bool -> term * term -> thm
   end;
 
 functor HypsubstFun(Data: HYPSUBST_DATA): HYPSUBST = 
 struct
 
 local open Data in
 
 fun REPEATN 0 tac = all_tac
   | REPEATN n tac = Tactic(fn state =>
                            tapply(tac THEN REPEATN (n-1) tac,  state));
-
-local
-  val T = case #1 (types_sorts rev_cut_eq) ("a",0) of
-	      Some T => T
-   	    | None   => error"No such variable in rev_cut_eq"
-in
-  fun liftvar inc paramTs = Var(("a",inc), paramTs ---> incr_tvar inc T);
-end;
 
 exception EQ_VAR;
 
 fun loose (i,t) = 0 mem add_loose_bnos(t,i,[]);
 

   It's not safe to substitute for a variable free in the premises,
     but how could we check for this?*)
 fun inspect_pair bnd (t,u) =
   case (Pattern.eta_contract t, Pattern.eta_contract u) of
        (Bound i, _) => if loose(i,u) then raise Match 
-		       else (t, asm_rl)
+		       else sym		(*eliminates t*)
      | (_, Bound i) => if loose(i,t) then raise Match 
-		       else (u, sym)
+		       else asm_rl	(*eliminates u*)
      | (Free _, _) => if bnd orelse Logic.occs(t,u) then raise Match 
-		      else (t, asm_rl)
+		      else sym		(*eliminates t*)
      | (_, Free _) => if bnd orelse Logic.occs(u,t) then raise Match 
-		      else (u, sym) 
+		      else asm_rl	(*eliminates u*)
      | _ => raise Match;
 
- (* Extracts the name of the variable on the left (resp. right) of an equality
-   assumption.  Returns the rule asm_rl (resp. sym). *)
-fun eq_var bnd (Const("all",_) $ Abs(_,_,t)) = eq_var bnd t
-  | eq_var bnd (Const("==>",_) $ A $ B) = 
-	(inspect_pair bnd (dest_eq A) 
-	        (*Match comes from inspect_pair or dest_eq*)
-	 handle Match => eq_var bnd B)
-  | eq_var bnd _ = raise EQ_VAR;
-
-(*Lift and instantiate a rule wrt the given state and subgoal number *)
-fun lift_instpair (state, i, t, rule) =
-  let val {maxidx,sign,...} = rep_thm state
-      val (_, _, Bi, _) = dest_state(state,i)
-      val params = Logic.strip_params Bi
-      val var = liftvar (maxidx+1) (map #2 params)
-      and u   = Unify.rlist_abs(rev params, t)
-      and cterm = cterm_of sign
-  in cterm_instantiate [(cterm var, cterm u)] (lift_rule (state,i) rule)
-  end;
-
-fun eres_instpair_tac t rule i = STATE (fn state => 
-	   compose_tac (true, lift_instpair (state, i, t, rule),
-			length(prems_of rule)) i);
-
-val ssubst = sym RS subst;
+(*Locates a substitutable variable on the left (resp. right) of an equality
+   assumption.  Returns the number of intervening assumptions, paried with
+   the rule asm_rl (resp. sym). *)
+fun eq_var bnd =
+  let fun eq_var_aux k (Const("all",_) $ Abs(_,_,t)) = eq_var_aux k t
+	| eq_var_aux k (Const("==>",_) $ A $ B) = 
+	      ((k, inspect_pair bnd (dest_eq A))
+		      (*Exception Match comes from inspect_pair or dest_eq*)
+	       handle Match => eq_var_aux (k+1) B)
+	| eq_var_aux k _ = raise EQ_VAR
+  in  eq_var_aux 0  end;
 
 (*Select a suitable equality assumption and substitute throughout the subgoal
   Replaces only Bound variables if bnd is true*)
 fun gen_hyp_subst_tac bnd i = DETERM (STATE(fn state =>
       let val (_,_,Bi,_) = dest_state(state,i)
 	  val n = length(Logic.strip_assums_hyp Bi) - 1
-	  val (t,symopt) = eq_var bnd Bi
-      in eres_instpair_tac t (symopt RS rev_cut_eq) i  THEN
-         REPEATN n (etac rev_mp i) THEN
-	 etac ssubst i THEN REPEATN n (rtac imp_intr i)
+	  val (k,symopt) = eq_var bnd Bi
+      in 
+	 EVERY [REPEATN k (etac rev_mp i),
+		etac revcut_rl i,
+		REPEATN (n-k) (etac rev_mp i),
+		etac (symopt RS subst) i,
+		REPEATN n (rtac imp_intr i)]
       end
       handle THM _ => no_tac | EQ_VAR => no_tac));
 
 (*Substitutes for Free or Bound variables*)
 val hyp_subst_tac = gen_hyp_subst_tac false;