(* OK: *)

Lemma degree_L1_split_x_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 dx:= MF.degree m x in
y0 = Iter (cF m) j x ->
i < j < dx - 1 ->
expf m x y0 ->
inv_hmap m1 -> MF.degree_aux m1 x (j - i) = j + 1.