author  wenzelm 
Wed, 28 Dec 2011 13:00:51 +0100  
changeset 46003  c0fe5e8e4864 
parent 38500  d5477ee35820 
child 51798  ad3a241def73 
permissions  rwrr 
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(* Title: FOL/intprover.ML 
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Author: Lawrence C Paulson, Cambridge University Computer Laboratory 
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Copyright 1992 University of Cambridge 
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A naive prover for intuitionistic logic 

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Renamed structure Int (intuitionistic prover) to IntPr to prevent clash
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BEWARE OF NAME CLASHES WITH CLASSICAL TACTICS  use IntPr.fast_tac ... 
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Completeness (for propositional logic) is proved in 

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Roy Dyckhoff. 

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ContractionFree Sequent Calculi for Intuitionistic Logic. 

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J. Symbolic Logic 57(3), 1992, pages 795807. 
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The approach was developed independently by Roy Dyckhoff and L C Paulson. 

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*) 
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signature INT_PROVER = 

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sig 

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val best_tac: int > tactic 

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val best_dup_tac: int > tactic 
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val fast_tac: int > tactic 
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val inst_step_tac: int > tactic 

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val safe_step_tac: int > tactic 

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val safe_brls: (bool * thm) list 

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val safe_tac: tactic 

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val step_tac: int > tactic 

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val step_dup_tac: int > tactic 
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val haz_brls: (bool * thm) list 
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val haz_dup_brls: (bool * thm) list 
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end; 
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Renamed structure Int (intuitionistic prover) to IntPr to prevent clash
paulson
parents:
2572
diff
changeset

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structure IntPr : INT_PROVER = 
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struct 
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(*Negation is treated as a primitive symbol, with rules notI (introduction), 

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not_to_imp (converts the assumption ~P to P>False), and not_impE 

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(handles double negations). Could instead rewrite by not_def as the first 

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step of an intuitionistic proof. 

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*) 

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val safe_brls = sort (make_ord lessb) 
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[ (true, @{thm FalseE}), (false, @{thm TrueI}), (false, @{thm refl}), 
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(false, @{thm impI}), (false, @{thm notI}), (false, @{thm allI}), 

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(true, @{thm conjE}), (true, @{thm exE}), 

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(false, @{thm conjI}), (true, @{thm conj_impE}), 

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(true, @{thm disj_impE}), (true, @{thm disjE}), 

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(false, @{thm iffI}), (true, @{thm iffE}), (true, @{thm not_to_imp}) ]; 

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val haz_brls = 

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[ (false, @{thm disjI1}), (false, @{thm disjI2}), (false, @{thm exI}), 
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(true, @{thm allE}), (true, @{thm not_impE}), (true, @{thm imp_impE}), (true, @{thm iff_impE}), 

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(true, @{thm all_impE}), (true, @{thm ex_impE}), (true, @{thm impE}) ]; 

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val haz_dup_brls = 
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[ (false, @{thm disjI1}), (false, @{thm disjI2}), (false, @{thm exI}), 
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(true, @{thm all_dupE}), (true, @{thm not_impE}), (true, @{thm imp_impE}), (true, @{thm iff_impE}), 

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(true, @{thm all_impE}), (true, @{thm ex_impE}), (true, @{thm impE}) ]; 

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(*0 subgoals vs 1 or more: the p in safep is for positive*) 
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val (safe0_brls, safep_brls) = 

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List.partition (curry (op =) 0 o subgoals_of_brl) safe_brls; 
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(*Attack subgoals using safe inferences  matching, not resolution*) 

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val safe_step_tac = FIRST' [eq_assume_tac, 

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eq_mp_tac, 
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bimatch_tac safe0_brls, 

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hyp_subst_tac, 

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bimatch_tac safep_brls] ; 

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(*Repeatedly attack subgoals using safe inferences  it's deterministic!*) 

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FOL/intprover/safe_tac: now uses REPEAT_DETERM_FIRST instead of REPEAT_DETERM
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val safe_tac = REPEAT_DETERM_FIRST safe_step_tac; 
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(*These steps could instantiate variables and are therefore unsafe.*) 

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val inst_step_tac = 

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assume_tac APPEND' mp_tac APPEND' 

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biresolve_tac (safe0_brls @ safep_brls); 

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(*One safe or unsafe step. *) 

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fun step_tac i = FIRST [safe_tac, inst_step_tac i, biresolve_tac haz_brls i]; 

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fun step_dup_tac i = FIRST [safe_tac, inst_step_tac i, biresolve_tac haz_dup_brls i]; 
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(*Dumb but fast*) 
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val fast_tac = SELECT_GOAL (DEPTH_SOLVE (step_tac 1)); 

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(*Slower but smarter than fast_tac*) 

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val best_tac = 

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SELECT_GOAL (BEST_FIRST (has_fewer_prems 1, size_of_thm) (step_tac 1)); 

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(*Uses all_dupE: allows multiple use of universal assumptions. VERY slow.*) 
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val best_dup_tac = 

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SELECT_GOAL (BEST_FIRST (has_fewer_prems 1, size_of_thm) (step_dup_tac 1)); 

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end; 
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