(* Was raising stack overflow in 8.4 and assertion failed in future 8.5 *)
Set Implicit Arguments.
(** Reflexive-transitive closure ( R* ) *)
Inductive rtclosure (A : Type) (R : A-> A->Prop) : A->A->Prop :=
| rtclosure_refl : forall x,
rtclosure R x x
| rtclosure_step : forall y x z,
R x y -> rtclosure R y z -> rtclosure R x z.
(* bug goes away if rtclosure_step is commented out *)
(** The closure of the trivial binary relation [eq] *)
Definition tr (A:Type) := rtclosure (@eq A).
(** The bug *)

Lemma bug : forall A B (l t:list A) (r s:list B),
length l = length r ->
tr (combine l r) (combine t s) -> tr l t.