intros a b p q s Eqd Z0 H'; inversion_clear H'.
absurd (ltT ltM b a); auto.
apply ltT_not_eqT; auto; apply eqT_sym; auto.
case Z0; auto.
apply pX_inj; auto.
apply uniq_minusp with (l := (p, q)); auto.
absurd (ltT ltM a b); auto.
Qed.

(* Specifications: *)
Theorem minuspf_inv1_eq :
forall (a b : Term A n) (p q : list (Term A n)),
ltT ltM b a -> pX a (minuspf p (pX b q)) = minuspf (pX a p) (pX b q).