(* IDEM, FOR nf_L0L1 : *)

Lemma inv_hmap_L0L1:forall (m:fmap)(x y x' y':dart),
let m1:= L (L m zero x y) one x' y' in
let m2:= L (L m one x' y') zero x y in
inv_hmap m1 -> inv_hmap m2.