Lemma cF_L1_y0: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 let dy0 := MF.degree m y0 in ~expf m x y0 -> Iter (cF m1) (dx + dy0) x = x.