proposition: Theorem sub_term : forall A B t, t ⊩ A -> A ⊆ B -> t ⊩ B.
proof: Proof. intros A B t Ht HAB. start. apply Ht. now apply HAB. Qed.
imports: RelationClasses Morphisms ClassicalRealizability.ShallowEmbedding ClassicalRealizability.Tactics ClassicalRealizability.BasicResults