Theorem degree_L1_merge_x_others: forall(m:fmap)(x y z:dart), let m1:= L m one x y in let y0 := cA m zero y in inv_hmap m1 -> exd m z -> ~expf m x y0 -> ~expf m x z -> ~expf m y0 z -> MF.degree m1 z = MF.degree m z.