(* OK! *)

Lemma degree_L1_split_y_1_aux:
forall(m:fmap)(x y:dart)(j i: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 + 1 + i < dx ->
expf m x y0 ->
inv_hmap m1 ->
MF.degree_aux m1 y_1 (dx - (j + 1 + i)) = dx - (j + 1).