proposition: Lemma olast_cons : forall a (x y : a) ys, olast (x :: y :: ys) = olast (y :: ys).
proof: Proof. intros a x y. induction ys as [|? xs IHxs]; trivial. Qed.
imports: Coq.Sorting.Sorted Coq.Sorting.Permutation Category.Lib Category.Theory.Functor Category.Theory.Coq.Functor Category.Theory.Coq.Functor.Proofs Category.Theory.Coq.List Category.Theory.Coq.Maybe