intros a b c; (case a; case b; case c).
intros x c0 x0 c1 x1 c2; generalize c0 c1 c2; case x; case x0; case x1;
simpl in |- *; auto.
intros a0 l a1 l0 a2 l1 H' H'0 H'1 H'2 H'3.
elim ppc_is_ppcm with (1 := cs) (a := a1) (b := a2); auto.
apply canonical_nzeroP with (ltM := ltM) (p := l0); auto.
apply canonical_nzeroP with (ltM := ltM) (p := l1); auto.
Qed.
Definition Cb : poly A0 eqA ltM -> list (poly A0 eqA ltM) -> Prop.
intros H'; case H'.
intros x H'0 Q;
exact (CombLinear A A0 eqA plusA multA eqA_dec n ltM ltM_dec Q x).
Defined.

Theorem Cb_id :
forall (a : poly A0 eqA ltM) (Q : list (poly A0 eqA ltM)), In a Q -> Cb a Q.