(*========================================================= cF / L, expf / L, CNS ===========================================================*)
(* expf IS AN EQUIVALENCE (NEW PLACE): *)

Lemma cF_I:forall(m:fmap)(x z:dart)(u:tag)(p:point),
inv_hmap m -> prec_I m x -> exd m z -> x <> z ->
(cF (I m x u p) z = cF m z).