(* Title: Provers/make_elim.ML
ID: $Id$
Author: Lawrence C Paulson, Cambridge University Computer Laboratory
Copyright 2000 University of Cambridge
Classical version of Tactic.make_elim
In classical logic, we can make stronger elimination rules using this version.
For instance, the HOL rule injD is transformed into
[| inj ?f; ~ ?W ==> ?f ?x = ?f ?y; ?x = ?y ==> ?W |] ==> ?W
while Tactic.make_elim would yield the weaker rule
[| inj ?f; ?f ?x = ?f ?y; ?x = ?y ==> PROP ?W |] ==> PROP ?W
Such rules can cause Fast_tac to fail and Blast_tac to report "PROOF FAILED"
*)
signature MAKE_ELIM_DATA =
sig
val classical : thm (* (~P ==> P) ==> P *)
end;
functor Make_Elim_Fun(Data: MAKE_ELIM_DATA) =
struct
local
val cla_dist_concl = prove_goal (the_context ())
"[| ~Z_ ==> PROP X_; PROP Y_ ==> Z_; PROP X_ ==> PROP Y_ |] ==> Z_"
(fn [premx,premz,premy] =>
([(rtac Data.classical 1),
(etac (premx RS premy RS premz) 1)]))
fun compose_extra nsubgoal (tha,i,thb) =
Seq.list_of (bicompose false (false,tha,nsubgoal) i thb)
in
fun make_elim rl =
let val revcut_rl' = incr_indexes_wrt [] [] [] [rl] revcut_rl
fun making (i,rl) =
case compose_extra 2 (cla_dist_concl,i,rl) of
[] => rl (*terminates by clash of variables!*)
| rl'::_ => making (i+1,rl')
in making (2, hd (compose_extra 1 (rl, 1, revcut_rl'))) end
handle (*in default, use the previous version, which never fails*)
THM _ => Tactic.make_elim rl | Empty => Tactic.make_elim rl;
end
end;