unfold nf in |- *.
intros p aP;
case
(Reducef A A0 A1 eqA plusA invA minusA multA divA cs eqA_dec n ltM ltM_dec
os aP p).
intros x; case x; simpl in |- *; auto.
intros x0 c H'; inversion H'.
red in H0.
red in |- *; red in |- *.
intros q0; intros H'0; auto.
cut (~ zeroP (A:=A) A0 eqA (n:=n) (unit (mks A A0 eqA n ltM x0 c)));
[ intros nZd | idtac ]; auto.
apply
H0
with
(q := mults (A:=A) multA (n:=n)
(divTerm (A:=A) (A0:=A0) (eqA:=eqA) divA (n:=n)
(T1 A1 n) (b:=unit (mks A A0 eqA n ltM x0 c)) nZd) q0);
auto.
apply reduce_mults_invf with (1 := cs); auto.
apply unit_T1; auto.
apply unit_nZ; auto.
Qed.

Theorem nf_red :
forall (a : poly A0 eqA ltM) (aP aQ : list (poly A0 eqA ltM)),
incl aP aQ -> red (nf a aP) aQ -> red a aQ.