(* IT IS DIFFRENT FROM x: *)

Lemma diff_x10:forall(m:fmap)(x y:dart),
inv_hmap m -> prec_L m one x y ->
let m1:= L m one x y in
let y0 := cA m zero y in
let dx := MF.degree m x in
~expf m x y0 ->
Iter (cF m1) dx x <> x.