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

(* Specifications: *)
Theorem minusP_inv2 :
forall (a b : Term A n) (p q s : list (Term A n)),
minusP (pX a p) (pX b q) s ->
ltT ltM a b -> s = pX (invTerm (A:=A) invA (n:=n) b) (minuspf (pX a p) q).