(* OK: "HINGES" BEFORE B0 *)

Lemma expf_xb0_xh0_1:forall (m:fmap)(x:dart),
inv_hmap m -> exd m x ->
let x0 := cA m zero x in
let x_1:= cA_1 m one 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 xb0 xh0_1.