intros p q; try assumption.
apply minusP_is_plusP_mults with (p := p) (q := q); auto.
Qed.
Hint Resolve minuspf_is_pluspf_mults.

(* Specifications: *)
Theorem pO_minusP_inv1 :
forall p q : list (Term A n),
minusP (pO A n) p q ->
q = mults (A:=A) multA (n:=n) (invTerm (A:=A) invA (n:=n) (T1 A1 n)) p.