proposition: Lemma join_ub_3_l x y z : x ≤ x ⊔ y ⊔ z.
proof: Proof. transitivity (x ⊔ y); now apply join_ub_l. Qed.
imports: MathClasses.interfaces.abstract_algebra MathClasses.interfaces.orders MathClasses.orders.maps MathClasses.theory.lattices