(* 1. CASE ~expf m x y0: FACE MERGING *)
(* FIRST, SOME LEMMAS: *)
(* OK: *)
Open Scope nat_scope.

Lemma degree_y0_y_1:forall(m:fmap)(x y:dart),
inv_hmap m -> prec_L m one x y ->
let y0 := cA m zero y in
let y_1:= cA_1 m one y in
MF.degree m y0 = MF.degree m y_1.