(* IT SEEMS TO HAVE A PROBLEM WITH :  MA0.expo1_dec : forall (m : fmap) (z t : dart), inv_hmap m -> exd m z -> {MA0.expo1 m z t} + {~ MA0.expo1 m z t} *)
(* WE ALSO HAVE (EASILY): *)

Lemma bottom_B0: forall(m:fmap)(z:dart),
inv_hmap m -> exd m z ->
bottom (B m zero z) zero z = bottom m zero z.