(* OK: *)

Lemma nf_L0L1_IXB: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 ->
let x_1 := cA_1 m one x in
let y_0 := cA_1 m zero y in
let y'0 := cA m zero y' in
let x'1 := cA m one x' in
let y'0b := cA (L m zero x y) zero y' in
let x_1b := cA_1 (L m one x' y') one x in
~ expf m x_1 y ->
~ expf m x' y'0 ->
expf (L m zero x y) x' y'0b ->
~ expf (L m one x' y') x_1b y ->
x <> y' -> y_0 = y' ->
False.