(* ANCIEN VERSION, WITHOUT nc_Br1: Lemma Jordan1:forall(m:fmap)(x x':dart), inv_hmap m -> planar m -> let l:= cons x x' lam in ring m l -> nc (Br m l) = nc m + 1. *)
(*======================================================= PRELIMINARIES FOR THE GENERAL CASE =======================================================*)
(* OK: *)

Lemma expf_expf_B:forall (m:fmap)(x z t: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 m z t -> expf (B m zero x) z t.