diff --git a/crf-chain1-constrained.cabal b/crf-chain1-constrained.cabal
--- a/crf-chain1-constrained.cabal
+++ b/crf-chain1-constrained.cabal
@@ -1,5 +1,5 @@
 name:               crf-chain1-constrained
-version:            0.4.0
+version:            0.5.0
 synopsis:           First-order, constrained, linear-chain conditional random fields
 description:
     The library provides efficient implementation of the first-order,
@@ -24,7 +24,7 @@
 license:            BSD3
 license-file:       LICENSE
 cabal-version:      >= 1.6
-copyright:          Copyright (c) 2012 IPI PAN
+copyright:          Copyright (c) 2012-2018 Jakub Waszczuk, IPI PAN
 author:             Jakub Waszczuk
 maintainer:         waszczuk.kuba@gmail.com
 stability:          experimental
diff --git a/src/Data/CRF/Chain1/Constrained/Core.hs b/src/Data/CRF/Chain1/Constrained/Core.hs
--- a/src/Data/CRF/Chain1/Constrained/Core.hs
+++ b/src/Data/CRF/Chain1/Constrained/Core.hs
@@ -23,6 +23,7 @@
 , AVec (..)
 , fromList
 , fromSet
+, toAscList
 
 -- * Features
 , Feature (..)
@@ -78,6 +79,11 @@
 fromSet = AVec . U.fromList . S.toAscList
 {-# INLINE fromSet #-}
 
+-- | Convert AVec to an ascending list.
+toAscList :: (Ord a, U.Unbox a) => AVec a -> [a]
+toAscList = U.toList . unAVec
+{-# INLINE toAscList #-}
+
 -- | A word represented by a list of its observations
 -- and a list of its potential label interpretations.
 data X
@@ -166,7 +172,7 @@
             0 -> SFeature <$> get
             1 -> TFeature <$> get <*> get
             2 -> OFeature <$> get <*> get
-	    _ -> error "Binary Feature: unknown identifier"
+            _ -> error "Binary Feature: unknown identifier"
 
 
 -- | Is it a 'SFeature'?
diff --git a/src/Data/CRF/Chain1/Constrained/DAG.hs b/src/Data/CRF/Chain1/Constrained/DAG.hs
--- a/src/Data/CRF/Chain1/Constrained/DAG.hs
+++ b/src/Data/CRF/Chain1/Constrained/DAG.hs
@@ -1,4 +1,3 @@
-
 {-# LANGUAGE RecordWildCards #-}
 
 -- | The module provides first-order, linear-chain conditional random fields
@@ -17,6 +16,7 @@
 , SentL
 
 -- ** Tagging
+, Config (..)
 , tag
 , marginals
 -- , tagK
@@ -28,13 +28,16 @@
 ) where
 
 import           Prelude hiding (Word)
-import qualified Data.Vector as V
+-- import qualified Data.Vector as V
+import qualified Data.Set as S
 import qualified Data.Number.LogFloat as L
 
 -- import qualified Data.CRF.Chain1.Constrained.DAG.Dataset.Internal as DAG
 import qualified Data.DAG as DAG
 import           Data.DAG (DAG)
 
+import qualified Data.CRF.Chain1.Constrained.Core as Core
+import qualified Data.CRF.Chain1.Constrained.Model as Model
 -- import           Data.CRF.Chain1.Constrained.Dataset.External
 import           Data.CRF.Chain1.Constrained.DAG.Dataset.External
 -- import           Data.CRF.Chain1.Constrained.DAG.Dataset.External (WordL(..))
@@ -44,19 +47,32 @@
 import           Data.CRF.Chain1.Constrained.DAG.Feature.Hidden
 import           Data.CRF.Chain1.Constrained.DAG.Train
 import qualified Data.CRF.Chain1.Constrained.DAG.Inference as I
-import qualified Data.CRF.Chain1.Constrained.Dataset.Internal as Int
+-- import qualified Data.CRF.Chain1.Constrained.Dataset.Internal as Int
 
 
+-- | Tagging configuration.
+data Config a = Config
+  { blackSet :: S.Set a
+    -- ^ Blacklisted tags
+  }
+
+
 -- | Determine the most probable label sequence within the context of the
 -- given sentence using the model provided by the 'CRF'.
-tag :: (Ord a, Ord b) => CRF a b -> Sent a b -> DAG () b
-tag CRF{..} sent
+tag 
+  :: (Ord a, Ord b)
+  => Config b
+  -> CRF a b
+  -> Sent a b
+  -> DAG () b
+tag Config{..} crf0 sent
     = onWords
     . fmap (decodeLabel codec)
     . I.tag model
     . C.encodeSent codec
     $ sent
   where
+    CRF{..} = blackList blackSet crf0
     -- handle unknown labels; otherwise, the type of `tag`s result
     -- would be `DAG () (Maybe b)`
     onWords labeled =
@@ -73,14 +89,15 @@
 -- (up to the way the set of all interpretations is constructed).
 -- In particular, if no interpretation with probability > 0 is found
 -- for an unknown word, its set of chosen labels will remain empty.
-marginals :: (Ord a, Ord b) => CRF a b -> Sent a b -> SentL a b
-marginals CRF{..} sent
+marginals :: (Ord a, Ord b) => Config b -> CRF a b -> Sent a b -> SentL a b
+marginals Config{..} crf0 sent
   = fmap decodeChosen
   . DAG.zipE sent
   . I.marginals model
   . C.encodeSent codec
   $ sent
   where
+    CRF{..} = blackList blackSet crf0
     decodeChosen (word, chosen) =
       mkWordL word prob
       where
@@ -115,3 +132,26 @@
 -- -- | Convert the sequential representation to DAG-based one.
 -- dagSent :: Int.Xs -> DAG.DAG () Int.X
 -- dagSent = DAG.fromList . V.toList
+
+
+------------------------------------------------------
+-- Blacklisting tags
+------------------------------------------------------
+
+
+-- | Blacklist the given set of tags, so that they are never proposed for
+-- OOV segments.
+blackList :: (Ord b) => S.Set b -> CRF a b -> CRF a b
+blackList blackSet CRF{..} = CRF
+  { codec = codec 
+  , model = newModel
+  }
+  where
+    newModel = model {Model.r0 = newR0}
+    r0Set = S.fromList . Core.toAscList $ Model.r0 model
+    newR0 = Core.fromSet $ r0Set `S.difference` blackSetEncoded
+    blackSetEncoded 
+      = S.fromList
+      . map (C.encodeLabel codec)
+      . S.toList
+      $ blackSet
diff --git a/src/Data/CRF/Chain1/Constrained/DAG/Dataset/External.hs b/src/Data/CRF/Chain1/Constrained/DAG/Dataset/External.hs
--- a/src/Data/CRF/Chain1/Constrained/DAG/Dataset/External.hs
+++ b/src/Data/CRF/Chain1/Constrained/DAG/Dataset/External.hs
@@ -9,7 +9,7 @@
 -- import qualified Data.Set as S
 -- import qualified Data.Map as M
 
-import qualified Data.DAG as DAG
+-- import qualified Data.DAG as DAG
 import           Data.DAG (DAG)
 -- import qualified Data.CRF.Chain1.Constrained.DAG.Dataset.Internal as DAG
 -- import           Data.CRF.Chain1.Constrained.DAG.Dataset.Internal (DAG)
diff --git a/src/Data/CRF/Chain1/Constrained/DAG/Feature/Hidden.hs b/src/Data/CRF/Chain1/Constrained/DAG/Feature/Hidden.hs
--- a/src/Data/CRF/Chain1/Constrained/DAG/Feature/Hidden.hs
+++ b/src/Data/CRF/Chain1/Constrained/DAG/Feature/Hidden.hs
@@ -16,7 +16,7 @@
 import           Data.DAG (DAG)
 import qualified Data.DAG as DAG
 
-import           Data.CRF.Chain1.Constrained.Core (AVec, X, Y, Lb, Feature)
+import           Data.CRF.Chain1.Constrained.Core (AVec, X, Lb, Feature)
 import qualified Data.CRF.Chain1.Constrained.Core as C
 
 -- import Data.CRF.Chain1.Constrained.Dataset.Internal
diff --git a/src/Data/CRF/Chain1/Constrained/DAG/Inference.hs b/src/Data/CRF/Chain1/Constrained/DAG/Inference.hs
--- a/src/Data/CRF/Chain1/Constrained/DAG/Inference.hs
+++ b/src/Data/CRF/Chain1/Constrained/DAG/Inference.hs
@@ -24,7 +24,7 @@
 
 import Control.Applicative ((<$>))
 import Data.Maybe (catMaybes)
-import Data.List (maximumBy, sort, sortBy)
+import Data.List (maximumBy, sortBy)
 import Data.Function (on)
 import qualified Data.Set as S
 import qualified Data.Array as A
@@ -50,7 +50,7 @@
 import qualified Data.CRF.Chain1.Constrained.Core as C
 import qualified Data.CRF.Chain1.Constrained.Intersect as I
 
-import           Data.CRF.Chain1.Constrained.DAG.Feature (featuresIn)
+-- import           Data.CRF.Chain1.Constrained.DAG.Feature (featuresIn)
 
 import Debug.Trace (trace)
 
@@ -60,7 +60,7 @@
 ---------------------------------------------
 
 
--- | TODO.
+-- | Label index.
 type LbIx       = Int
 
 
@@ -168,7 +168,7 @@
     [ i
     | i <- DAG.dagEdges dag
     , DAG.isInitialEdge i dag ]
-  withMem psi alpha i
+  withMem psi alpha' i
     | i == snd bounds = const u'
     | i `S.member` initialSet = \j ->
         let x = lbOn crf (DAG.edgeLabel i dag) j
@@ -178,22 +178,22 @@
         in  psi j * ((u - v x) + w x)
     where
       u = safeSum
-        [ alpha iMinus1 k
+        [ alpha' iMinus1 k
         | iMinus1 <- DAG.prevEdges i dag
         , (k, _) <- lbIxs crf dag iMinus1 ]
       v x = safeSum
-        [ alpha iMinus1 k
+        [ alpha' iMinus1 k
         | iMinus1 <- DAG.prevEdges i dag
         , (k, _) <- I.intersect (Md.prevIxs crf x) (lbVec crf dag iMinus1) ]
       w x = safeSum
-        [ alpha iMinus1 k * Md.valueL crf ix
+        [ alpha' iMinus1 k * Md.valueL crf ix
         | iMinus1 <- DAG.prevEdges i dag
         , (k, ix) <- I.intersect (Md.prevIxs crf x) (lbVec crf dag iMinus1) ]
       -- Note that if `i == snd bounds` then `i` does not refer to any existing
       -- edge, hence the need to introduce `u'` which does almost the same thing
       -- as `u`.
       u' = safeSum
-        [ alpha iMinus1 k
+        [ alpha' iMinus1 k
         | iMinus1 <- DAG.dagEdges dag
         , DAG.isFinalEdge iMinus1 dag
         , (k, _) <- lbIxs crf dag iMinus1 ]
@@ -213,10 +213,10 @@
     [ i
     | i <- DAG.dagEdges dag
     , DAG.isFinalEdge i dag ]
-  withMem beta i
+  withMem beta' i
     | i `S.member` finalSet = const 1
     | i == fst bounds = const $ safeSum
-      [ beta iPlus1 k * psi iPlus1 k
+      [ beta' iPlus1 k * psi iPlus1 k
         * Md.sgValue crf (lbOn crf (DAG.edgeLabel iPlus1 dag) k)
       | iPlus1 <- DAG.dagEdges dag
       , DAG.isInitialEdge iPlus1 dag
@@ -229,19 +229,19 @@
       -- Instead of simply adding `1` to `i` (i.e., `i + 1`),
       -- we need to find the identifiers of the succeeding edges.
       u = safeSum
-        [ beta iPlus1 k * psi iPlus1 k
+        [ beta' iPlus1 k * psi iPlus1 k
         | iPlus1 <- DAG.nextEdges i dag
         , (k, _ ) <- lbIxs crf dag iPlus1 ]
       -- `y` is the label on position `i`, we are looking for
       -- matching labels on the position `i+1`.
       v y = safeSum
-        [ beta iPlus1 k * psi iPlus1 k
+        [ beta' iPlus1 k * psi iPlus1 k
         | iPlus1 <- DAG.nextEdges i dag
         , (k, _ ) <- I.intersect (Md.nextIxs crf y) (lbVec crf dag iPlus1) ]
       -- `y` is the label on position `i`, we are looking for
       -- matching labels on the position `i+1`.
       w y = safeSum
-        [ beta iPlus1 k * psi iPlus1 k * Md.valueL crf ix
+        [ beta' iPlus1 k * psi iPlus1 k * Md.valueL crf ix
         | iPlus1 <- DAG.nextEdges i dag
         , (k, ix) <- I.intersect (Md.nextIxs crf y) (lbVec crf dag iPlus1) ]
 
@@ -288,7 +288,7 @@
       error $ "edgeProb1: infinite -- " ++ show [up1, up2, down, down'] -- ++ "; " ++ show (k, x)
   | otherwise = up1 * up2 / down
   where
-    isInf x = isInfinite (L.logFromLogFloat x :: Double)
+    isInf v = isInfinite (L.logFromLogFloat v :: Double)
     up1 = alpha k x
     up2 = beta k x
     down = zxBeta dag beta
@@ -462,7 +462,7 @@
 accuracy :: Md.Model -> [DAG a (X, Y)] -> Double
 accuracy crf dataset =
     let k = numCapabilities
-    	parts = partition k dataset
+        parts = partition k dataset
         xs = parMap rseq (goodAndBad' crf) parts
         (good, bad) = F.foldl' add (0, 0) xs
         add (g, b) (g', b') = (g + g', b + b')
diff --git a/src/Data/CRF/Chain1/Constrained/DAG/Probs.hs b/src/Data/CRF/Chain1/Constrained/DAG/Probs.hs
--- a/src/Data/CRF/Chain1/Constrained/DAG/Probs.hs
+++ b/src/Data/CRF/Chain1/Constrained/DAG/Probs.hs
@@ -12,18 +12,18 @@
 ) where
 
 
-import Control.Applicative ((<$>))
-import Data.Maybe (catMaybes)
-import Data.List (maximumBy, sort, sortBy)
-import Data.Function (on)
+-- import Control.Applicative ((<$>))
+-- import Data.Maybe (catMaybes)
+-- import Data.List (maximumBy, sort, sortBy)
+-- import Data.Function (on)
 import qualified Data.Set as S
 import qualified Data.Array as A
 -- import qualified Data.Vector as V
 import qualified Data.Vector.Unboxed as U
-import qualified Data.Foldable as F
+-- import qualified Data.Foldable as F
 
 import Control.Parallel.Strategies (rseq, parMap)
-import Control.Parallel (par, pseq)
+-- import Control.Parallel (par, pseq)
 import GHC.Conc (numCapabilities)
 import qualified Data.Number.LogFloat as L
 
@@ -40,7 +40,7 @@
 import qualified Data.CRF.Chain1.Constrained.Core as C
 import qualified Data.CRF.Chain1.Constrained.Intersect as I
 
-import           Data.CRF.Chain1.Constrained.DAG.Feature (featuresIn)
+-- import           Data.CRF.Chain1.Constrained.DAG.Feature (featuresIn)
 import qualified Data.CRF.Chain1.Constrained.DAG.Inference as Inf
 
 
@@ -66,8 +66,9 @@
 
 -- | Vector of labels and the corresponding probabilities on the given edge of
 -- the sentence.
+-- TODO: get rid of the _crf argument.
 lbVec :: Md.Model -> DAG a (X, Y) -> EdgeID -> AVec (Lb, Double)
-lbVec crf dag edgeID =
+lbVec _crf dag edgeID =
   case DAG.edgeLabel edgeID dag of
     (_, y) -> C._unY y
 {-# INLINE lbVec #-}
@@ -134,7 +135,7 @@
     [ i
     | i <- DAG.dagEdges dag
     , DAG.isInitialEdge i dag ]
-  withMem psi alpha i
+  withMem psi alpha' i
     | i == snd bounds = const u'                    -- <= TO CHECK
     | i `S.member` initialSet = \j ->
         let (x, _) = lbOn crf dag i j
@@ -144,23 +145,23 @@
         in  psi j * ((u - v x) + w x)
     where
       u = safeSum
-        [ alpha iMinus1 k
+        [ alpha' iMinus1 k
         | iMinus1 <- DAG.prevEdges i dag
         , (k, _) <- lbIxs crf dag iMinus1 ]
       v x = safeSum
-        [ alpha iMinus1 k
+        [ alpha' iMinus1 k
         | iMinus1 <- DAG.prevEdges i dag
         , (k, _) <-
             I.intersect (Md.prevIxs crf x) (xify $ lbVec crf dag iMinus1) ]
       w x = safeSum
-        [ alpha iMinus1 k * Md.valueL crf ix
+        [ alpha' iMinus1 k * Md.valueL crf ix
         | iMinus1 <- DAG.prevEdges i dag
         , (k, ix) <- I.intersect (Md.prevIxs crf x) (xify $ lbVec crf dag iMinus1) ]
       -- Note that if `i == snd bounds` then `i` does not refer to any existing
       -- edge, hence the need to introduce `u'` which does almost the same thing
       -- as `u`.
       u' = safeSum
-        [ alpha iMinus1 k
+        [ alpha' iMinus1 k
         | iMinus1 <- DAG.dagEdges dag
         , DAG.isFinalEdge iMinus1 dag
         , (k, _) <- lbIxs crf dag iMinus1 ]
diff --git a/src/Data/CRF/Chain1/Constrained/DAG/Train.hs b/src/Data/CRF/Chain1/Constrained/DAG/Train.hs
--- a/src/Data/CRF/Chain1/Constrained/DAG/Train.hs
+++ b/src/Data/CRF/Chain1/Constrained/DAG/Train.hs
@@ -25,13 +25,13 @@
 
 
 import Control.Applicative ((<$>), (<*>))
-import qualified Control.Arrow as Arr
+-- import qualified Control.Arrow as Arr
 import Control.Monad (when)
 import System.IO (hSetBuffering, stdout, BufferMode (..))
 import Data.Binary (Binary, put, get)
 import qualified Data.Set as S
 import qualified Data.Map as M
-import qualified Data.Vector as V
+-- import qualified Data.Vector as V
 import qualified Data.Vector.Unboxed as U
 import qualified Data.Foldable as F
 import qualified Numeric.SGD.Momentum as SGD
@@ -47,7 +47,7 @@
 import           Data.CRF.Chain1.Constrained.Core (X, Y, Lb, AVec, Feature)
 import qualified Data.CRF.Chain1.Constrained.Core as C
 import qualified Data.CRF.Chain1.Constrained.Model as Md
-import qualified Data.CRF.Chain1.Constrained.Dataset.Internal as Int
+-- import qualified Data.CRF.Chain1.Constrained.Dataset.Internal as Int
 
 import qualified Data.CRF.Chain1.Constrained.DAG.Dataset.Codec as Cd
 import qualified Data.CRF.Chain1.Constrained.DAG.Dataset.External as E
@@ -157,8 +157,8 @@
 --       report $ U.map (*0.5) para
 --       report $ U.map (*0.1) para
   where
-    report para = do
-      let crf = model {Md.values = para}
+    report paraNow = do
+      let crf = model {Md.values = paraNow}
       llh <- show
         . LogFloat.logFromLogFloat
         . P.parLikelihood crf
diff --git a/src/Data/CRF/Chain1/Constrained/DP.hs b/src/Data/CRF/Chain1/Constrained/DP.hs
--- a/src/Data/CRF/Chain1/Constrained/DP.hs
+++ b/src/Data/CRF/Chain1/Constrained/DP.hs
@@ -20,12 +20,12 @@
           $ map f
           $ range bounds
 
-down2 :: (A.Ix i, A.Ix j) => (j, j) -> (j -> (i, i)) -> (j -> i -> e)
-      -> j -> i -> e
-down2 bounds1 bounds2 f = (!) down' where
-    down' = A.listArray bounds1
-        [ down1 (bounds2 i) (f i)
-        | i <- range bounds1 ]
+-- down2 :: (A.Ix i, A.Ix j) => (j, j) -> (j -> (i, i)) -> (j -> i -> e)
+--       -> j -> i -> e
+-- down2 bounds1 bounds2 f = (!) down' where
+--     down' = A.listArray bounds1
+--         [ down1 (bounds2 i) (f i)
+--         | i <- range bounds1 ]
 
 -- | 2-dimensional computation using dynamic programming.
 flexible2
diff --git a/src/Data/CRF/Chain1/Constrained/Dataset/Codec.hs b/src/Data/CRF/Chain1/Constrained/Dataset/Codec.hs
--- a/src/Data/CRF/Chain1/Constrained/Dataset/Codec.hs
+++ b/src/Data/CRF/Chain1/Constrained/Dataset/Codec.hs
@@ -20,6 +20,7 @@
 , encodeSentL'Cn
 , encodeSentL
 
+, encodeLabel
 , encodeLabels
 , decodeLabel
 , decodeLabels
@@ -102,8 +103,8 @@
     r' <- mapM encodeLbU $ S.toList $ lbs $ word w
     let x = mkX x' r'
     y  <- mkY <$> sequence
-    	[ (,) <$> encodeLbU lb <*> pure pr
-	| (lb, pr) <- (M.toList . unProb) (choice w) ]
+        [ (,) <$> encodeLbU lb <*> pure pr
+        | (lb, pr) <- (M.toList . unProb) (choice w) ]
     return (x, y)
 
 -- | Encodec the labeled word and do *not* update the codec.
@@ -113,8 +114,8 @@
     r' <- mapM encodeLbN . S.toList . lbs $ word w
     let x = mkX x' r'
     y  <- mkY <$> sequence
-    	[ (,) <$> encodeLbN lb <*> pure pr
-	| (lb, pr) <- (M.toList . unProb) (choice w) ]
+        [ (,) <$> encodeLbN lb <*> pure pr
+        | (lb, pr) <- (M.toList . unProb) (choice w) ]
     return (x, y)
 
 -- | Encode the word and update the codec.
@@ -177,6 +178,10 @@
 -- | Encode the dataset with the codec.
 encodeData :: (Ord a, Ord b) => Codec a b -> [Sent a b] -> [Xs]
 encodeData = map . encodeSent
+
+-- | Encode the label.
+encodeLabel :: Ord b => Codec a b -> b -> Lb
+encodeLabel codec = C.evalCodec codec . encodeLbN
 
 -- | Decode the label.
 decodeLabel :: Ord b => Codec a b -> Lb -> Maybe b
diff --git a/src/Data/CRF/Chain1/Constrained/Feature/Hidden.hs b/src/Data/CRF/Chain1/Constrained/Feature/Hidden.hs
--- a/src/Data/CRF/Chain1/Constrained/Feature/Hidden.hs
+++ b/src/Data/CRF/Chain1/Constrained/Feature/Hidden.hs
@@ -16,7 +16,7 @@
 import qualified Data.Vector as V
 
 import Data.CRF.Chain1.Constrained.Dataset.Internal
-import Data.CRF.Chain1.Constrained.Feature
+-- import Data.CRF.Chain1.Constrained.Feature
 
 -- | Hidden 'OFeature's which can be constructed based on the dataset.
 -- The default set of potential interpretations is used for all unknown words.
diff --git a/src/Data/CRF/Chain1/Constrained/Feature/Present.hs b/src/Data/CRF/Chain1/Constrained/Feature/Present.hs
--- a/src/Data/CRF/Chain1/Constrained/Feature/Present.hs
+++ b/src/Data/CRF/Chain1/Constrained/Feature/Present.hs
@@ -15,7 +15,7 @@
 import qualified Data.Vector as V
 
 import Data.CRF.Chain1.Constrained.Dataset.Internal
-import Data.CRF.Chain1.Constrained.Feature
+-- import Data.CRF.Chain1.Constrained.Feature
 
 -- | 'OFeature's which occur in the dataset.
 presentOFeats :: [(Xs, Ys)] -> [Feature]
diff --git a/src/Data/CRF/Chain1/Constrained/Inference.hs b/src/Data/CRF/Chain1/Constrained/Inference.hs
--- a/src/Data/CRF/Chain1/Constrained/Inference.hs
+++ b/src/Data/CRF/Chain1/Constrained/Inference.hs
@@ -78,7 +78,7 @@
     bounds i
         | i == V.length xs = (0, 0)
         | otherwise = (0, lbNum crf xs i - 1)
-    withMem psi alpha i
+    withMem psi alpha' i
         | i == V.length xs = const u
         | i == 0 = \j ->
             let x = lbOn crf (xs V.! i) j
@@ -88,13 +88,13 @@
             in  psi j * ((u - v x) + w x)
       where
         u = sum
-            [ alpha (i-1) k
+            [ alpha' (i-1) k
             | (k, _) <- lbIxs crf xs (i-1) ]
         v x = sum
-            [ alpha (i-1) k
+            [ alpha' (i-1) k
             | (k, _) <- intersect (prevIxs crf x) (lbVec crf xs (i-1)) ]
         w x = sum
-            [ alpha (i-1) k * valueL crf ix
+            [ alpha' (i-1) k * valueL crf ix
             | (k, ix) <- intersect (prevIxs crf x) (lbVec crf xs (i-1)) ]
 
 -- | Backward table computation.
@@ -105,10 +105,10 @@
     bounds i
         | i == 0    = (0, 0)
         | otherwise = (0, lbNum crf xs (i-1) - 1)
-    withMem psi beta i
+    withMem psi beta' i
         | i == V.length xs = const 1
         | i == 0 = const $ sum
-            [ beta (i+1) k * psi k
+            [ beta' (i+1) k * psi k
             * sgValue crf (lbOn crf (xs V.! i) k)
             | (k, _) <- lbIxs crf xs i ]
         | otherwise = \j ->
@@ -116,13 +116,13 @@
             in  (u - v y) + w y
       where
         u = sum
-            [ beta (i+1) k * psi k
+            [ beta' (i+1) k * psi k
             | (k, _ ) <- lbIxs crf xs i ]
         v y = sum
-            [ beta (i+1) k * psi k
+            [ beta' (i+1) k * psi k
             | (k, _ ) <- intersect (nextIxs crf y) (lbVec crf xs i) ]
         w y = sum
-            [ beta (i+1) k * psi k * valueL crf ix
+            [ beta' (i+1) k * psi k * valueL crf ix
             | (k, ix) <- intersect (nextIxs crf y) (lbVec crf xs i) ]
 
 zxBeta :: ProbArray -> L.LogFloat
diff --git a/src/Data/CRF/Chain1/Constrained/Model.hs b/src/Data/CRF/Chain1/Constrained/Model.hs
--- a/src/Data/CRF/Chain1/Constrained/Model.hs
+++ b/src/Data/CRF/Chain1/Constrained/Model.hs
@@ -25,8 +25,8 @@
 import Data.List (groupBy, sort)
 import Data.Function (on)
 import Data.Binary
-import qualified Data.Vector.Generic.Base as G
-import qualified Data.Vector.Generic.Mutable as G
+-- import qualified Data.Vector.Generic.Base as G
+-- import qualified Data.Vector.Generic.Mutable as G
 import qualified Data.Set as Set
 import qualified Data.Map as M
 import qualified Data.Vector.Unboxed as U
@@ -71,7 +71,7 @@
     , r0        :: AVec Lb
     -- | Singular feature index for the given label.  Index is equall to -1
     -- if feature is not present in the model.
-    , sgIxsV 	:: U.Vector FeatIx
+    , sgIxsV    :: U.Vector FeatIx
     -- | Set of labels for the given observation which, together with the
     -- observation, constitute an observation feature of the model.
     , obIxsV    :: V.Vector (AVec LbIx)