src/FOL/intprover.ML

concept for exceptions

(*  Title:      FOL/int-prover
    ID:         $Id$
    Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
    Copyright   1992  University of Cambridge

A naive prover for intuitionistic logic

BEWARE OF NAME CLASHES WITH CLASSICAL TACTICS -- use IntPr.fast_tac ...

Completeness (for propositional logic) is proved in 

Roy Dyckhoff.
Contraction-Free Sequent Calculi for Intuitionistic Logic.
J. Symbolic Logic  57(3), 1992, pages 795-807.

The approach was developed independently by Roy Dyckhoff and L C Paulson.
*)

signature INT_PROVER = 
  sig
  val best_tac: int -> tactic
  val best_dup_tac: int -> tactic
  val fast_tac: int -> tactic
  val inst_step_tac: int -> tactic
  val safe_step_tac: int -> tactic
  val safe_brls: (bool * thm) list
  val safe_tac: tactic
  val step_tac: int -> tactic
  val step_dup_tac: int -> tactic
  val haz_brls: (bool * thm) list
  val haz_dup_brls: (bool * thm) list
  end;


structure IntPr : INT_PROVER   = 
struct

(*Negation is treated as a primitive symbol, with rules notI (introduction),
  not_to_imp (converts the assumption ~P to P-->False), and not_impE
  (handles double negations).  Could instead rewrite by not_def as the first
  step of an intuitionistic proof.
*)
val safe_brls = sort (make_ord lessb)
    [ (true, thm "FalseE"), (false, thm "TrueI"), (false, thm "refl"),
      (false, thm "impI"), (false, thm "notI"), (false, thm "allI"),
      (true, thm "conjE"), (true, thm "exE"),
      (false, thm "conjI"), (true, thm "conj_impE"),
      (true, thm "disj_impE"), (true, thm "disjE"), 
      (false, thm "iffI"), (true, thm "iffE"), (true, thm "not_to_imp") ];

val haz_brls =
    [ (false, thm "disjI1"), (false, thm "disjI2"), (false, thm "exI"), 
      (true, thm "allE"), (true, thm "not_impE"), (true, thm "imp_impE"), (true, thm "iff_impE"),
      (true, thm "all_impE"), (true, thm "ex_impE"), (true, thm "impE") ];

val haz_dup_brls =
    [ (false, thm "disjI1"), (false, thm "disjI2"), (false, thm "exI"),
      (true, thm "all_dupE"), (true, thm "not_impE"), (true, thm "imp_impE"), (true, thm "iff_impE"),
      (true, thm "all_impE"), (true, thm "ex_impE"), (true, thm "impE") ];

(*0 subgoals vs 1 or more: the p in safep is for positive*)
val (safe0_brls, safep_brls) =
    List.partition (curry (op =) 0 o subgoals_of_brl) safe_brls;

(*Attack subgoals using safe inferences -- matching, not resolution*)
val safe_step_tac = FIRST' [eq_assume_tac,
                            eq_mp_tac,
                            bimatch_tac safe0_brls,
                            hyp_subst_tac,
                            bimatch_tac safep_brls] ;

(*Repeatedly attack subgoals using safe inferences -- it's deterministic!*)
val safe_tac = REPEAT_DETERM_FIRST safe_step_tac;

(*These steps could instantiate variables and are therefore unsafe.*)
val inst_step_tac =
  assume_tac APPEND' mp_tac APPEND' 
  biresolve_tac (safe0_brls @ safep_brls);

(*One safe or unsafe step. *)
fun step_tac i = FIRST [safe_tac, inst_step_tac i, biresolve_tac haz_brls i];

fun step_dup_tac i = FIRST [safe_tac, inst_step_tac i, 
			    biresolve_tac haz_dup_brls i];

(*Dumb but fast*)
val fast_tac = SELECT_GOAL (DEPTH_SOLVE (step_tac 1));

(*Slower but smarter than fast_tac*)
val best_tac = 
  SELECT_GOAL (BEST_FIRST (has_fewer_prems 1, size_of_thm) (step_tac 1));

(*Uses all_dupE: allows multiple use of universal assumptions.  VERY slow.*)
val best_dup_tac = 
  SELECT_GOAL (BEST_FIRST (has_fewer_prems 1, size_of_thm) (step_dup_tac 1));


end;