src/Tools/induction.ML

avoid ambiguities on native Windows, such as / vs. /cygdrive/c/cygwin;

(*  Title:      Tools/induction.ML
    Author:     Tobias Nipkow, TU Muenchen

Alternative proof method "induction" that gives induction hypotheses the
name "IH".
*)

signature INDUCTION =
sig
  val induction_tac: Proof.context -> bool ->
    (binding option * (term * bool)) option list list ->
    (string * typ) list list -> term option list -> thm list option ->
    thm list -> int -> cases_tactic
end

structure Induction: INDUCTION =
struct

val ind_hypsN = "IH";

fun preds_of t =
  (case strip_comb t of
    (p as Var _, _) => [p]
  | (p as Free _, _) => [p]
  | (_, ts) => maps preds_of ts);

fun name_hyps (arg as ((cases, consumes), th)) =
  if not (forall (null o #2 o #1) cases) then arg
  else
    let
      val (prems, concl) = Logic.strip_horn (Thm.prop_of th);
      val prems' = drop consumes prems;
      val ps = preds_of concl;

      fun hname_of t =
        if exists_subterm (member (op aconv) ps) t
        then ind_hypsN else Rule_Cases.case_hypsN;

      val hnamess = map (map hname_of o Logic.strip_assums_hyp) prems';
      val n = Int.min (length hnamess, length cases);
      val cases' =
        map (fn (((cn, _), concls), hns) => ((cn, hns), concls))
          (take n cases ~~ take n hnamess);
    in ((cases', consumes), th) end;

val induction_tac = Induct.gen_induct_tac name_hyps;

val _ = Theory.local_setup (Induct.gen_induct_setup @{binding induction} induction_tac);

end