intros S D rho A B H. induction H. intros. subst. exists A1, A2. auto.
intros. subst.
inversion H; subst; destruct (IHmultipar _ _ eq_refl) as [B1 [B2 EQ]]; auto;
exists B1, B2; auto.
Qed.

Lemma multipar_CPi : forall S D A C, multipar S D A C -> forall A1 A2 A3 B, A = a_CPi (Eq A1 A2 A3) B -> exists B1 B2 B3 C2,
C = (a_CPi (Eq B1 B2 B3) C2).