(* filter and fcat *)

(* Specifications: *)
Lemma kfilt_fcat (p : pred K) (s1 s2 : fmap) :
kfilter p (fcat s1 s2) = fcat (kfilter p s1) (kfilter p s2).
Lemma kfilter_pred0 (s : fmap) : kfilter pred0 s = nil.
Lemma eq_in_kfilter p1 p2 s :
{in supp s, p1 =1 p2} -> kfilter p1 s = kfilter p2 s.