(* OK: *)

Lemma nf_L0L0_VI:forall (m:fmap)(x y x' y':dart),
let m1:= L (L m zero x y) zero x' y' in
let m2:= L (L m zero x' y') zero x y in
inv_hmap m1 ->
let x_1  := cA_1 m one x in
let x'_1 := cA_1 m one x' in
expf m x_1 y ->
~ expf m x'_1 y' ->
~ expf (L m zero x' y') x_1 y ->
~ expf (L m zero x y) x'_1 y' ->
nf m1 = nf m2.