(* CONSEQUENTLY: THE "BIG" RESULT *)
Open Scope Z_scope.

(* Specifications: *)
Theorem nf_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 -> nf m1 = nf m2.