intros p; apply uniq_minusp with (l := (pO A n, p)); auto.
Qed.

(* Specifications: *)
Theorem minuspf_eq_inv2 :
forall (a : Term A n) (p q : list (Term A n)),
canonical A0 eqA ltM (pX a p) ->
canonical A0 eqA ltM (pX a q) ->
eqP A eqA n (pX (invTerm (A:=A) invA (n:=n) a) (minuspf p q))
(minuspf p (pX a q)).