proposition: Lemma subtype_eqtype : forall A B, A ⊆ B -> B ⊆ A -> A ≈ B.
proof: Proof. intros A B HAB HBA s. split; intro Hπ; now (apply HAB || apply HBA). Qed.
imports: RelationClasses Morphisms ClassicalRealizability.ShallowEmbedding ClassicalRealizability.Tactics ClassicalRealizability.BasicResults