(* j-SUCCS OF y BY cF_L1, FOR j < DEGREE OF y, ARE INVARIANT: *)

Lemma cF_L1_y_1_y0_aux:forall(m:fmap)(x y:dart)(j:nat),
inv_hmap m -> prec_L m one x y ->
let m1:= L m one x y in
let y0 := cA m zero y in
let y_1 := cA_1 m one y in
let dx := MF.degree m x in
let dy_1 := MF.degree m y_1 in
~expf m x y0 ->
j <= dy_1 -1 ->
Iter (cF m1) (dx + j) x = Iter (cF m) j y_1.