(*=========================================================== expe AND bottom ============================================================*)
(* expo and between in an edge: *)
Definition expe(m:fmap)(z t:dart):=
MA0.expo m z t.
Definition betweene(m:fmap)(z v t:dart):=
MA0.between m z v t.
(* TO HAVE expe_bottom: *)

Lemma expe_bottom: forall(m:fmap)(z t:dart),
inv_hmap m -> MA0.expo m z t ->
bottom m zero z = bottom m zero t.