proposition: Lemma combine_cons : forall x r y s, combine (x::r) (y::s) = (x,y)::(combine r s).
proof: Proof. Proof using. auto. Qed.
imports: Coq.Classes.Morphisms TLC(LibTactics LibLogic LibReflect LibOperation LibProd LibOption LibNat LibInt LibWf LibMonoid LibRelation)