proposition: Lemma ct_lex: forall u v w u' v' w', ct u v w -> ct u' v' w' -> ct (lex u u') (lex v v') (lex w w').
proof: Proof. intros u v w u' v' w' H H'. inversion_clear H; inversion_clear H'; ct; destruct w; ct; destruct w'; ct. Qed.
imports: Bool PeanoNat BinPos Orders OrdersEx MSetInterface