(* SYMMETRIC, OK: *)

Lemma expf_expf_L0_1:forall (m:fmap)(x y z:dart)(i:nat),
inv_hmap (L m zero x y) -> exd m z ->
let x_1 := cA_1 m one x in
let t := Iter (cF m) i z in
expf m x_1 y -> ~ expf m x_1 z ->
expf (L m zero x y) z t.