Lemma diff_y_1_y0:forall(m:fmap)(x y:dart)(j:nat), 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 y_1 := cA_1 m one y in let dx := MF.degree m x in let dy0 := MF.degree m y0 in ~expf m x y0 -> j <= dy0 -1 -> Iter (cF m1) (dx + j) x <> x.