(* DISCONNECTION CRITERION: VERY USEFUL *)

(* Specifications: *)
Theorem disconnect_planar_criterion_B0:forall (m:fmap)(x:dart),
inv_hmap m -> planar m -> succ m zero x ->
let y := A m zero x in
let x0 := bottom m zero x in
(expf m y x0 <-> ~eqc (B m zero x) x y).