author  lcp 
Thu, 06 Apr 1995 11:04:37 +0200  
changeset 1005  65188e520024 
parent 702  98fc1a8e832a 
child 1459  d12da312eff4 
permissions  rwrr 
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(* Title: FOL/intprover 
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ID: $Id$ 

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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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BEWARE OF NAME CLASHES WITH CLASSICAL TACTICS  use Int.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 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 haz_brls: (bool * thm) list 

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end; 

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structure Int : 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 lessb 

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[ (true,FalseE), (false,TrueI), (false,refl), 

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(false,impI), (false,notI), (false,allI), 

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(true,conjE), (true,exE), 

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(false,conjI), (true,conj_impE), 

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(true,disj_impE), (true,ex_impE), 

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(true,disjE), (false,iffI), (true,iffE), (true,not_to_imp) ]; 

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val haz_brls = 

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[ (false,disjI1), (false,disjI2), (false,exI), 

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(true,allE), (true,not_impE), (true,imp_impE), (true,iff_impE), 

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(true,all_impE), (true,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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partition (apl(0,op=) 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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98fc1a8e832a
FOL/intprover/safe_tac: now uses REPEAT_DETERM_FIRST instead of REPEAT_DETERM
lcp
parents:
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diff
changeset

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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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(*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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end; 

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