(* OK! *)

Lemma degree_L1_split_y_1:
forall(m:fmap)(x y:dart)(j:nat),
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
y0 = Iter (cF m) j x ->
j < dx - 1 ->
expf m x y0 ->
inv_hmap m1 ->
MF.degree m1 y_1 = dx - (j + 1).