(*========================================================= face cutting/joining, hmap deconnection after L0/B0... ===========================================================*)
(* FACE JOINING/CUTTING AFTER B0: OK *)

Theorem face_cut_join_criterion_B0:forall (m:fmap)(x:dart),
inv_hmap m -> succ m zero x ->
let y := A m zero x in
let x0 := bottom m zero x in
(expf m y x0 <-> ~expf (B m zero x) y x0).