src/FOLP/hypsubst.ML
 author wenzelm Mon, 21 Aug 2017 17:15:26 +0200 changeset 66475 d8e0fd64216f parent 60754 02924903a6fd child 69593 3dda49e08b9d permissions -rw-r--r--
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(*  Title:      FOLP/hypsubst.ML
Author:     Martin D Coen, Cambridge University Computer Laboratory

Original version of Provers/hypsubst.  Cannot use new version because it
relies on the new simplifier!

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_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 : Proof.context -> int -> tactic
val hyp_subst_tac       : Proof.context -> int -> tactic
(*exported purely for debugging purposes*)
val eq_var              : bool -> term -> int * thm
val inspect_pair        : bool -> term * term -> thm
end;

functor Hypsubst(Data: HYPSUBST_DATA): HYPSUBST =
struct

local open Data in

exception EQ_VAR;

(*It's not safe to substitute for a constant; consider 0=1.
It's not safe to substitute for x=t[x] since x is not eliminated.
It's not safe to substitute for a Var; what if it appears in other goals?
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 (Envir.eta_contract t, Envir.eta_contract u) of
(Bound i, _) =>
if loose_bvar1 (u, i) then raise Match
else sym         (*eliminates t*)
| (_, Bound i) =>
if loose_bvar (t, i) then raise Match
else asm_rl      (*eliminates u*)
| (Free _, _) =>
if bnd orelse Logic.occs (t, u) then raise Match
else sym          (*eliminates t*)
| (_, Free _) =>
if bnd orelse Logic.occs(u,t) then raise Match
else asm_rl       (*eliminates u*)
| _ => raise Match);

(*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(@{const_name Pure.all},_) \$ Abs(_,_,t)) = eq_var_aux k t
| eq_var_aux k (Const(@{const_name Pure.imp},_) \$ 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 ctxt = SUBGOAL(fn (Bi,i) =>
let val n = length(Logic.strip_assums_hyp Bi) - 1
val (k,symopt) = eq_var bnd Bi
in
DETERM
(EVERY [REPEAT_DETERM_N k (eresolve_tac ctxt [rev_mp] i),
eresolve_tac ctxt [revcut_rl] i,
REPEAT_DETERM_N (n-k) (eresolve_tac ctxt [rev_mp] i),
eresolve_tac ctxt [symopt RS subst] i,
REPEAT_DETERM_N n (resolve_tac ctxt [imp_intr] i)])
end
handle THM _ => no_tac | EQ_VAR => no_tac);