intros p.
rewrite (minusP_refl p p (minuspf p p)); auto.
Qed.

Theorem mults_comp_minuspf :
forall (a : Term A n) (p q : list (Term A n)),
canonical A0 eqA ltM p ->
canonical A0 eqA ltM q ->
~ zeroP (A:=A) A0 eqA (n:=n) a ->
eqP A eqA n
(minuspf (mults (A:=A) multA (n:=n) a p) (mults (A:=A) multA (n:=n) a q))
(mults (A:=A) multA (n:=n) a (minuspf p q)).