src/Tools/induction.ML
author nipkow
Tue Sep 20 05:47:11 2011 +0200 (2011-09-20)
changeset 45014 0e847655b2d8
child 56506 c1f04411d43f
permissions -rw-r--r--
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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