prop_representative :: Ord a => Set a -> Property
prop_representative s = 
    not (null s) ==>
    (fromJust $ getRepresentative s) `member` s
prop_representative :: Ord a => Set a -> Property
prop_representative s = 
    not (null s) ==>
    (fromJust $ getRepresentative s) `member` s
prop_representative s = 
    not (null s) ==>
    (fromJust $ getRepresentative s) `member` s