(*========================================================= CONSEQUENCES / B0 ===========================================================*)
(* OK: VERY USEFUL IN JORDAN CURVE THEOREM *)

Theorem expf_not_expf_B0: forall (m:fmap)(x:dart),
inv_hmap m -> succ m zero x ->
let x_1:= cA_1 m one x in
let x0 := cA m zero x in
let xb0 := bottom m zero x in
(expf (B m zero x) x_1 x0 <-> ~expf m x0 xb0).