-- | Determines whether a particular element is in the 'Closed'
-- set. If the element is in the set, this operation is always
-- defined. If it is not and the set is unbounded, this operation is
-- undefined (see 'memberWithin'). It's reasonable to think of this
-- operation as
-- 
-- @
--   let omega = succ omega in memberWithin omega
-- @
member :: (Hashable a, Eq a) => a -> Closed a -> Bool
member a = fst . member' a
member :: (Hashable a, Eq a) => a -> Closed a -> Bool
member a = fst . member' a
member a = fst . member' a