Section unitOrd.
Let ordtt (x y : unit ) := false.
(* in a sorted list, the last element is maximal *)
(* and the maximal element is last *)

Lemma sorted_max_key_last (A : ordType) (s : seq A) x y :
sorted oleq s -> x \in s ->
(forall z, z \in s -> oleq z x) -> last y s = x.