Lemma expf_B0_CS_1_b_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 xh0 := top m zero x in let xh0_1 := cA_1 m one xh0 in expf m x0 xb0 -> betweenf m xh0_1 z x0 -> expf (B m zero x) xh0_1 z.