(* expf / B *)
(* ========== 1ST PART OF CS: CASE expf m x0 xb0 =========== *)
(* OK : *)

Lemma expf_B0_CS_1_a_prel2:forall (m:fmap)(x z:dart),
inv_hmap m -> succ m zero x ->
let x0 := cA m zero x in
let xb0 := bottom m zero x in
let x_1 := cA_1 m one x in
expf m x0 xb0 -> betweenf m x_1 z xb0
-> expf (B m zero x) x_1 z.