diff --git a/NLP/Scores.hs b/NLP/Scores.hs
--- a/NLP/Scores.hs
+++ b/NLP/Scores.hs
@@ -55,7 +55,7 @@
 import qualified Data.Set as Set
 import qualified Data.Map as Map
 import Prelude hiding (sum)
-
+import Data.Strict.Tuple (Pair((:!:)))
 import NLP.Scores.Internals
 
 
@@ -104,11 +104,11 @@
 mi :: (Ord a, Ord b) => Counts a b -> Double
 mi (Counts cxy cx cy) =
   let n = Map.foldl' (+) 0 cxy
-      cell (P x y) nxy = 
+      cell (x :!: y) nxy = 
         let nx = cx Map.! x
             ny = cy Map.! y
         in  nxy / n * logBase 2 (nxy * n / nx / ny)
-  in sum [ cell (P x y) nxy | (P x y, nxy) <- Map.toList cxy ]
+  in sum [ cell (x :!: y) nxy | (x :!: y, nxy) <- Map.toList cxy ]
 
 -- | Variation of information: VI(X,Y) = H(X) + H(Y) - 2 MI(X,Y)
 vi :: (Ord a, Ord b) => Counts a b -> Double
@@ -150,7 +150,7 @@
 -- | The mean of a sequence of numbers.
 mean :: (F.Foldable t, Fractional n, Real a) => t a -> n
 mean xs = 
-    let (P tot len) = F.foldl' (\(P s l) x -> (P (s+x) (l+1))) (P 0 0) xs
+    let (tot :!: len) = F.foldl' (\(s :!: l) x -> ((s+x) :!: (l+1))) (0 :!: 0) xs
     in realToFrac tot/len
 {-# SPECIALIZE mean :: [Double] -> Double #-}
 
@@ -189,15 +189,15 @@
 
 -- | Creates count table 'Counts'
 counts :: (Ord a, Ord b, T.Traversable t, F.Foldable s) => t a -> s b -> Counts a b
-counts xs = F.foldl' f empty . zipWithTF P xs . F.toList
-    where f cs@(Counts cxy cx cy) p@(P x y) = 
+counts xs = F.foldl' f empty . zipWithTF (:!:) xs . F.toList
+    where f cs@(Counts cxy cx cy) p@(x :!: y) = 
             cs { joint       = Map.insertWith' (+) p 1 cxy
                , marginalFst = Map.insertWith' (+) x 1 cx
                , marginalSnd = Map.insertWith' (+) y 1 cy }
 
 -- | Joint count
 countJoint :: (Ord a, Ord b) => a -> b -> Counts a b -> Count          
-countJoint x y = Map.findWithDefault 0 (P x y) . joint
+countJoint x y = Map.findWithDefault 0 (x :!: y) . joint
 -- | Count of first element
 countFst :: Ord k => k -> Counts k b -> Count
 countFst x = Map.findWithDefault 0 x . marginalFst
diff --git a/NLP/Scores/Internals.hs b/NLP/Scores/Internals.hs
--- a/NLP/Scores/Internals.hs
+++ b/NLP/Scores/Internals.hs
@@ -1,25 +1,24 @@
 module NLP.Scores.Internals
     ( Counts(..)
     , Count
-    , P(..)
     , empty
     , unionPlus
     )
 where
 import qualified Data.Map as Map
 import Data.Monoid
+import Data.Strict.Tuple
 
 -- | A count
 type Count = Double
 -- | Count table
 data Counts a b = 
   Counts 
-  { joint :: !(Map.Map (P a b) Count) -- ^ Counts of both components
+  { joint :: !(Map.Map (Pair a b) Count) -- ^ Counts of both components
   , marginalFst :: !(Map.Map a Count) -- ^ Counts of the first component
   , marginalSnd :: !(Map.Map b Count) -- ^ Counts of the second component
   } 
-data P a b = P !a !b deriving (Eq, Ord)
-
+  
 -- | The empty count table
 empty :: (Ord a, Ord b) => Counts a b
 empty = Counts Map.empty Map.empty Map.empty
diff --git a/nlp-scores.cabal b/nlp-scores.cabal
--- a/nlp-scores.cabal
+++ b/nlp-scores.cabal
@@ -7,7 +7,7 @@
 -- The package version. See the Haskell package versioning policy
 -- (http://www.haskell.org/haskellwiki/Package_versioning_policy) for
 -- standards guiding when and how versions should be incremented.
-Version:             0.6.0
+Version:             0.6.2
 
 -- A short (one-line) description of the package.
 Synopsis:            Scoring functions commonly used for evaluation in NLP and IR
@@ -29,7 +29,7 @@
 
 -- An email address to which users can send suggestions, bug reports,
 -- and patches.
-Maintainer:          gchrupala@lsv.uni-saarland.de
+Maintainer:          grzegorz.chrupala@gmail.com
 
 -- A copyright notice.
 -- Copyright:           
@@ -51,7 +51,7 @@
   Exposed-modules:     NLP.Scores, NLP.Scores.Internals
   
   -- Packages needed in order to build this package.
-  Build-depends:  base >= 3 && < 5 ,  containers >= 0.4.2
+  Build-depends:  base >= 3 && < 5 ,  containers >= 0.4.2 , strict >= 0.3
   -- Modules not exported by this package.
   -- Other-modules: