intros a b p q H' H1';
rewrite (plusP_inv3a a b p q (pluspf (pX a p) (pX b q)));
auto.
Qed.

Theorem pluspf_inv3b_eq :
forall a b p q,
eqT a b ->
~ zeroP (A:=A) A0 eqA (n:=n) (plusTerm (A:=A) plusA (n:=n) a b) ->
pX (plusTerm (A:=A) plusA (n:=n) a b) (pluspf p q) =
pluspf (pX a p) (pX b q).