diff --git a/non-negative.cabal b/non-negative.cabal
--- a/non-negative.cabal
+++ b/non-negative.cabal
@@ -1,5 +1,5 @@
 Name:             non-negative
-Version:          0.0.4
+Version:          0.0.5
 License:          GPL
 License-File:     LICENSE
 Author:           Henning Thielemann <haskell@henning-thielemann.de>
@@ -27,7 +27,7 @@
 Library
   Build-Depends: QuickCheck >= 1.0 && <2
   If flag(splitBase)
-    Build-Depends: base >= 2
+    Build-Depends: base >= 2 && < 5
   Else
     Build-Depends: base >= 1.0 && < 2
 
diff --git a/src/Numeric/NonNegative/Chunky.hs b/src/Numeric/NonNegative/Chunky.hs
--- a/src/Numeric/NonNegative/Chunky.hs
+++ b/src/Numeric/NonNegative/Chunky.hs
@@ -16,6 +16,9 @@
 which allows for co-recursive merges.
 -}
 module Numeric.NonNegative.Chunky
-   (T, fromChunks, fromNumber, toChunks, toNumber, zero, normalize, isNull, isPositive, ) where
+   (T, fromChunks, fromNumber, toChunks, toNumber,
+    zero, normalize, isNull, isPositive,
+    minMaxDiff,
+   ) where
 
 import Numeric.NonNegative.ChunkyPrivate
diff --git a/src/Numeric/NonNegative/ChunkyPrivate.hs b/src/Numeric/NonNegative/ChunkyPrivate.hs
--- a/src/Numeric/NonNegative/ChunkyPrivate.hs
+++ b/src/Numeric/NonNegative/ChunkyPrivate.hs
@@ -13,11 +13,13 @@
 module Numeric.NonNegative.ChunkyPrivate
    (T, fromChunks, fromNumber, toChunks, toNumber,
     zero, normalize, isNull, isPositive,
+    minMaxDiff,
     fromChunksUnsafe, toChunksUnsafe, ) where
 
 import qualified Numeric.NonNegative.Class as NonNeg
 import Control.Monad (liftM, liftM2)
 
+import qualified Data.Monoid as Mn
 import Test.QuickCheck (Arbitrary(..))
 
 {- |
@@ -87,12 +89,6 @@
      else error ("Numeric.NonNegative.Chunky."++funcName++": negative number")
 
 
-{- |
-In @glue x y == (z,r,b)@
-@z@ represents @min x y@,
-@r@ represents @max x y - min x y@,
-and @x<y  ==>  b@ or @x>y  ==>  not b@, for @x==y@ the value of b is arbitrary.
--}
 glue :: (NonNeg.C a) => [a] -> [a] -> ([a], [a], Bool)
 glue [] ys = ([], ys, True)
 glue xs [] = ([], xs, False)
@@ -104,6 +100,18 @@
               EQ -> (x, glue xs ys)
    in  (z:zs,rs,b)
 
+{- |
+In @minMaxDiff x y == (z,r,b)@
+@z@ represents @min x y@,
+@r@ represents @max x y - min x y@,
+and @x<y  ==>  b@ or @x>y  ==>  not b@,
+ for @x==y@ the value of b is arbitrary.
+-}
+minMaxDiff :: (NonNeg.C a) => T a -> T a -> (T a, T a, Bool)
+minMaxDiff (Cons xs) (Cons ys) =
+   let (zs, rs, b) = glue xs ys
+   in  (Cons zs, Cons rs, b)
+
 equalList :: (NonNeg.C a) => [a] -> [a] -> Bool
 equalList x y =
    let (_,r,_) = glue x y
@@ -142,7 +150,7 @@
       in  Cons (foldr sub x w)
 
 instance (NonNeg.C a) => Num (T a) where
-   (+)    = lift2 (++)
+   (+)    = Mn.mappend
    (Cons x) - (Cons y) =
       let (_,d,b) = glue x y
           d' = Cons d
@@ -153,6 +161,10 @@
    abs    = id
    signum = fromNumber . (\b -> if b then 1 else 0) . isPositive
 
+
+instance Mn.Monoid (T a) where
+   mempty = zero
+   mappend = lift2 (++)
 
 instance (NonNeg.C a, Arbitrary a) => Arbitrary (T a) where
    arbitrary = liftM Cons arbitrary