proposition: Lemma sub_Impl : forall A A' B B', A ⊆ A' -> B ⊆ B' -> A' → B ⊆ A → B'.
proof: Proof. intros A A' B B' HA HB. start. split. start. apply Ht. now apply HA. now apply HB. Qed.
imports: RelationClasses Morphisms ClassicalRealizability.ShallowEmbedding ClassicalRealizability.Tactics ClassicalRealizability.BasicResults