intros i a aP; elim aP.
simpl in |- *; case (foreigner_dec A A0 A1 eqA multA n ltM i a); auto.
intros H' Q H'0; inversion H'0.
intros a0 l H' Q; simpl in |- *.
case
(divp_dec _ _ _ _ _ _ _ _ _ cs n ltM
(ppcp A A0 A1 eqA plusA invA minusA multA divA cs n ltM i a) a0);
auto.
intros H'0 H'1; inversion H'1; auto.
left; exists a0; split; simpl in |- *; auto.
case
(divp_dec _ _ _ _ _ _ _ _ _ cs n ltM
(ppcp A A0 A1 eqA plusA invA minusA multA divA cs n ltM i a0) a);
auto.
generalize H'; clear H'; case (slice i a l); simpl in |- *; auto.
intros P H' H'0 H'1 H'2; inversion H'2.
intros P H' H'0 H'1 H'2; inversion H'2.
elim (H' P);
[ intros H'5; elim H'5; intros c E; elim E; intros H'6 H'7; clear E H'5
| intros H'5
| idtac ]; auto.
left; exists c; split; simpl in |- *; auto.
Qed.
Definition Tl : list (poly A0 eqA ltM) -> list (poly A0 eqA ltM) -> Prop.
exact (fun x y : list (poly A0 eqA ltM) => length x < length y).
Defined.

Theorem wf_Tl : well_founded Tl.
apply (wf_inverse_image _ _ lt (length (A:=poly A0 eqA ltM))); auto.