author  nipkow 
Tue, 20 Sep 2011 05:47:11 +0200  
changeset 45014  0e847655b2d8 
child 56506  c1f04411d43f 
permissions  rwrr 
45014
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New proof method "induction" that gives induction hypotheses the name IH.
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signature INDUCTION = 
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sig 
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val induction_tac: Proof.context > bool > (binding option * (term * bool)) option list list > 
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(string * typ) list list > term option list > thm list option > 
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thm list > int > cases_tactic 
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val setup: theory > theory 
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end 
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structure Induction: INDUCTION = 
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struct 
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val ind_hypsN = "IH"; 
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fun preds_of t = 
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(case strip_comb t of 
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(p as Var _, _) => [p] 
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 (p as Free _, _) => [p] 
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 (_, ts) => flat(map preds_of ts)) 
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fun name_hyps thy (arg as ((cases,consumes),th)) = 
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if not(forall (null o #2 o #1) cases) then arg 
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else 
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let 
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val (prems, concl) = Logic.strip_horn (prop_of th); 
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val prems' = drop consumes prems; 
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val ps = preds_of concl; 
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fun hname_of t = 
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if exists_subterm (member (op =) ps) t 
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then ind_hypsN else Rule_Cases.case_hypsN 
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val hnamess = map (map hname_of o Logic.strip_assums_hyp) prems' 
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val n = Int.min (length hnamess, length cases) 
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val cases' = map (fn (((cn,_),concls),hns) => ((cn,hns),concls)) 
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(take n cases ~~ take n hnamess) 
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in ((cases',consumes),th) end 
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val induction_tac = Induct.gen_induct_tac name_hyps 
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val setup = Induct.gen_induct_setup @{binding induction} induction_tac 
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end 
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43 