(* THEN, OK: *)

Theorem degree_L1_split_x_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
y_1 = Iter (cF m) j x ->
inv_hmap m1 ->
1 <= j <= dx -1 ->
expf m x y0 ->
MF.degree m1 x = j.