(* OK, BY INDUCTION ON i: *)

Lemma Iter_cF_L1_i: forall(m:fmap)(x y z:dart)(i:nat),
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 ->
Iter (cF m1) i z = Iter (cF m) i z.