insertMin x t
  = case t of
      Tip -> singleton x
      Bin _ y l r
          -> balanceL y (insertMin x l) r

{--------------------------------------------------------------------
  [merge l r]: merges two trees.
--------------------------------------------------------------------}
insertMin x t
  = case t of
      Tip -> singleton x
      Bin _ y l r
          -> balanceL y (insertMin x l) r

{--------------------------------------------------------------------
  [merge l r]: merges two trees.
--------------------------------------------------------------------}
insertMin x t
  = case t of
      Tip -> singleton x
      Bin _ y l r
          -> balanceL y (insertMin x l) r

{--------------------------------------------------------------------
  [merge l r]: merges two trees.
--------------------------------------------------------------------}