(* SYMMETRICALLY, USEFUL: *)

Lemma between_expf_L0_2:forall (m:fmap)(x y:dart)(i:nat),
inv_hmap (L m zero x y) ->
let y_0_1 := cF m y in
let x0 := cA m zero x in
let z := Iter (cF m) i y_0_1 in
betweenf m y_0_1 z x0 ->
expf (L m zero x y) y_0_1 z.