proposition: Lemma Sort_In_cons_3 : forall x l k e, Sort ((k,e)::l) -> In x l -> ~eq x k.
proof: Proof. inversion_clear 1; red; intros. destruct (Sort_Inf_NotIn H0 H1 (In_eq H2 H)). Qed.
imports: SetoidList Bool OrderedType OrdersLists RelationPairs Orders RelationClasses