----------------------------------------------------------------------------
-- Follower
-------------------------------------------------------------------------------

part :: (a -> Bool) -> HashSet a -> (HashSet a, HashSet a)
part p s = (S.filter p s, S.filter (not . p) s)
{-
part :: (a -> Bool) -> HashSet a -> (HashSet a, HashSet a)
part p s = (S.filter p s, S.filter (not . p) s)
part p s = (S.filter p s, S.filter (not . p) s)