(* TECHNICAL LEMMA: THE OTHER DEGREES ARE INCHANGED: *)

Lemma degree_L1_merge_x_others_aux:
forall(m:fmap)(x y z:dart)(n:nat),
let m1:= L m one x y in
let y0 := cA m zero y in
let dz:= MF.degree m z in
inv_hmap m1 -> exd m z -> ~expf m x y0 ->
~expf m x z -> ~expf m y0 z -> n < dz ->
MF.degree_aux m1 z (dz - n) = MF.degree_aux m z (dz - n).