(* TECHNICAL LEMMA: *)

Lemma degree_L1_merge_MAX:
forall(m:fmap)(x y:dart),
let m1:= L m one x y in
let y0 := cA m zero y in
inv_hmap m1 -> ~expf m x y0 ->
let MAX := MF.degree m x + MF.degree m y0 in
MF.degree_aux m1 x MAX = MAX.