Lemma expf_B0_CS_1_c_prel:forall (m:fmap)(x z:dart)(i:nat), inv_hmap m -> succ m zero x -> exd m z -> let x0 := cA m zero x in let xb0 := bottom m zero x in let x_1 := cA_1 m one x in let t:= Iter (cF m) i z in expf m x0 xb0 -> ~ expf m x_1 z -> expf (B m zero x) z t.