intros a b p q s H'; inversion_clear H'; intros.
absurd (ltT ltM a b); auto.
absurd (ltT ltM a b); auto.
absurd (ltT ltM a b); auto.
apply pX_inj; auto.
apply uniq_plusp with (l := (pX a p, q)); simpl in |- *; auto.
Qed.

(* Specifications: *)
Theorem plusP_inv3a :
forall a b p q s,
eqT a b ->
zeroP (A:=A) A0 eqA (n:=n) (plusTerm (A:=A) plusA (n:=n) a b) ->
plusP (pX a p) (pX b q) s -> s = pluspf p q.