proposition: Lemma Aeq_p1_NS_eq X s : Aeq (proj1_sig X) s -> X = NS s.
proof: Proof. destruct X as [t H1]. simpl. intros H2. unfold NS. apply PI_eq. rewrite <- H1. now apply CR2. Qed.
imports: Undecidability.FOL.Sets.Models(Aczel) Setoid Morphisms