Arguments eq_dec _ _ _ _ : simpl never.

Corollary upd_Znth_eq' : forall {A}{d: Inhabitant A} x (l1 l2 : list A) i (Hi : 0 <= i < Zlength l1)
(Hlen : Zlength l1 = Zlength l2)
(Heq : forall j, 0 <= j < Zlength l1 -> j <> i -> Znth j l1 = Znth j l2),
upd_Znth i l1 x = upd_Znth i l2 x.