unfold nf in |- *.
intros p aP; case p.
intros x c.
case
(Reducef A A0 A1 eqA plusA invA minusA multA divA cs eqA_dec n ltM ltM_dec
os aP (exist (fun l => canonical A0 eqA ltM l) x c));
auto.
unfold red in |- *; auto.
intros x0; case x0.
intros x1; case x1.
simpl in |- *; auto.
intros a l c0 H' H'0; inversion H'.
simpl in |- *.
change
(reducestar A A0 A1 eqA invA minusA multA divA eqA_dec n ltM ltM_dec aP
(mults (A:=A) multA (n:=n) (unit (mks A A0 eqA n ltM (a :: l) c0))
(a :: l)) (pO A n)) in H'0.
inversion H'0.
inversion H3.
inversion H7.
simpl in H0.
cut (~ zeroP (A:=A) A0 eqA (n:=n) (unit (mks A A0 eqA n ltM (pX a l) c0)));
[ intros nZd | idtac ]; auto.
case
(H0
(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 (pX a l) c0)) nZd) y));
auto.
apply reduce_mults_invf with (1 := cs); auto.
apply unit_T1; auto.
apply unit_nZ; auto.
Qed.

Theorem zerop_red :
forall (a : poly A0 eqA ltM) (aP : list (poly A0 eqA ltM)),
zerop (nf a aP) -> red a aP.