intros a b p q H'; elim H'; simpl in |- *; auto.
intros ma mb p0 q0 H'0 H'1 H'2 H'3 H'4 H'5 H'6 H'7.
cut (canonical A0 eqA ltM p0);
[ intros Op1 | apply canonical_imp_canonical with (a := ma); auto ].
cut (canonical A0 eqA ltM q0);
[ intros Op2 | apply canonical_imp_canonical with (a := mb); auto ].
cut (~ zeroP (A:=A) A0 eqA (n:=n) ma);
[ intros Z0 | apply canonical_nzeroP with (ltM := ltM) (p := p0); auto ].
cut (~ zeroP (A:=A) A0 eqA (n:=n) mb);
[ intros Z1 | apply canonical_nzeroP with (ltM := ltM) (p := q0); auto ].
auto.
Qed.

Theorem Dmult_is_mulpf :
forall (a : Term A n) (nZa : ~ zeroP (A:=A) A0 eqA (n:=n) a)
(p q : list (Term A n)),
canonical A0 eqA ltM p ->
canonical A0 eqA ltM q ->
eqP A eqA n (Dmult a nZa (mults (A:=A) multA (n:=n) a p) q)
(multpf A A0 eqA plusA multA eqA_dec n ltM ltM_dec p q).