Lemma diff_x_x10:forall(m:fmap)(x y:dart)(i:nat), inv_hmap m -> prec_L m one x y -> let y0 := cA m zero y in let dx := MF.degree m x in let m1:= L m one x y in ~expf m x y0 -> 0 < i <= dx - 1 -> Iter (cF m1) i x <> x.