{--------------------------------------------------------------------
  Split
--------------------------------------------------------------------}
-- | /O(log n)/. The expression (@'split' x set@) is a pair @(set1,set2)@
-- where @set1@ comprises the elements of @set@ less than @x@ and @set2@
-- comprises the elements of @set@ greater than @x@.
split :: Ord a => a -> Set a -> (Set a,Set a)
split _ Tip = (Tip,Tip)
split :: Ord a => a -> Set a -> (Set a,Set a)
split _ Tip = (Tip,Tip)
split _ Tip = (Tip,Tip)