diff --git a/COPYING.LESSER b/COPYING.LESSER
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--- /dev/null
+++ b/COPYING.LESSER
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+                   GNU LESSER GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
+
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diff --git a/Setup.hs b/Setup.hs
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+++ b/Setup.hs
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+import Distribution.Simple
+main = defaultMain
diff --git a/src/Data/Knot.hs b/src/Data/Knot.hs
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--- /dev/null
+++ b/src/Data/Knot.hs
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+{-
+    This file is part of tie-knot.
+
+    tie-knot is free software: you can redistribute it and/or modify it under
+    the terms of the GNU Lesser General Public License as published by the Free
+    Software Foundation, either version 3 of the License, or (at your option)
+    any later version.
+
+    tie-knot is distributed in the hope that it will be useful, but WITHOUT ANY
+    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+    FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for
+    more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with tie-knot.  If not, see <http://www.gnu.org/licenses/>.
+-}
+
+{-# LANGUAGE TypeFamilies, FlexibleContexts, FlexibleInstances #-}
+
+-- | Module for tying the knot on data structures that reference each other by
+-- some kind of keys. The 'tie' function replaces all such references with the actual
+-- value, creating possibly recursive or cyclic data structures.
+--
+-- The module re-exports a part of the fixpoint package.
+--
+-- An example how to construct a structure with circular dependencies:
+--
+-- > data Person = Person { name :: String, loves :: [Person] }
+-- > -- Define a variant of Person where the recursive type
+-- > -- is given as a parameter, and injection/projection functions.
+-- > instance Fixpoint Person where
+-- >   data Pre Person t = Loves { _name :: String, _loves :: [t] }
+-- >   inject ~(Loves n ps)    = Person n ps
+-- >   project ~(Person n ps)  = Loves n ps
+-- >
+-- > -- The easisest way to get 'Foldable' + 'Functor' is to implement
+-- > -- 'Traversable' and then just use the default implementations.
+-- > instance T.Traversable (Pre Person) where
+-- >     traverse f (Loves n ns) = Loves n <$> T.traverse f ns
+-- >
+-- > instance Functor (Pre Person) where
+-- >     fmap = T.fmapDefault
+-- > instance F.Foldable (Pre Person) where
+-- >     foldMap = T.foldMapDefault
+-- >
+-- > -- Let's create a person with cicrular dependencies:
+-- > alice :: Person
+-- > alice = fromJust . Map.lookup "Alice" .
+-- >             tie' . Map.fromList . map (\l -> (_name l, l)) $ lst
+-- >   where
+-- >     lst = [ Loves "Alice" ["Bob", "cat"]
+-- >           , Loves "Bob"   ["Alice"]
+-- >           -- you may disagree, but the cat thinks of itself as Person
+-- >           , Loves "cat"   ["cat"]
+-- >           ]
+module Data.Knot (tie, tie', isConsistent, RefMap, TieError(..), Fixpoint, Pre, inject, project) where
+
+import Control.Monad
+import Control.Monad.Error
+import qualified Data.Foldable as F
+import Data.Map (Map)
+import qualified Data.Map as Map
+import Data.Monoid
+import Data.Maybe
+
+import Data.Fixpoint
+
+-- | Represents a set of data 'v' that reference each other
+-- using keys of type 'k'.
+type RefMap k v = Map k (v k)
+
+-- | Possible errors when tying the knot.
+data TieError k
+    = MissingKey k k    -- ^ A value with key k1 referenced non-existent key k2.
+  deriving (Show, Eq, Ord)
+
+-- | Check the loader for consistency, i.e. if all referenced keys
+-- have a corresponding value. Values need to implement 'Foldable'
+-- that traverses over all referenced keys.
+isConsistent :: (Ord k, F.Foldable v, Functor v)
+    => RefMap k v                           -- ^ The loader to check.
+    -> Either (TieError k) (RefMap k v)     -- ^ The loader argument or an error.
+isConsistent l = maybe (Right l) Left . getFirst $
+        Map.foldrWithKey (\k -> mappend . keysOk k) mempty l
+  where
+    keysOk k = F.foldMap (\r -> First $ if (Map.member r l)
+                                                     then Nothing
+                                                     else (Just (MissingKey k r)) )
+
+-- | Helper function for anamorphisms.
+ana' :: Fixpoint t => (s -> Pre t s) -> Pre t s -> t
+ana' f = inject . fmap (ana f)
+
+-- | Ties the knot without checking consistency.
+-- If the references are inconsistent, an exception is raised.
+tie' :: (Ord k, Fixpoint v) => RefMap k (Pre v) -> Map k v
+tie' m = Map.map f m
+  where
+    -- (k -> v k) -> v k -> Fix v
+    f = ana' $ \k -> fromJust (Map.lookup k m)
+
+-- | Checks consistency by calling 'isConsistent' and then and ties the knot using 'tie''.
+tie :: (Ord k, F.Foldable (Pre v), Fixpoint v) => RefMap k (Pre v) -> Either (TieError k) (Map k v)
+tie = liftM tie' . isConsistent
diff --git a/tie-knot.cabal b/tie-knot.cabal
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+Name:                tie-knot
+Version:             0.1
+Synopsis:
+    "Ties the knot" on a given set of structures that reference each other by
+    keys.
+Description:
+    "Ties the knot" on a given set of structures that reference each other by
+    keys - replaces the keys with their respective values. Takes @Map k (v k)@
+    and converts into @Map k v'@ where @v'@ is the fixed point of @v@. See the
+    homepage for examples.
+Category:            Data Structures
+License:             LGPL
+License-file:        COPYING.LESSER
+Author:              Petr Pudlák
+Copyright:           (c) 2012 Petr Pudlák
+Maintainer:          Petr Pudlák <petr.mvd@gmail.com>
+Build-Type:          Simple
+Cabal-Version:       >=1.6
+Stability:           Experimental
+Homepage:            https://github.com/ppetr/tie-knot
+Bug-reports:         https://github.com/ppetr/tie-knot/issues
+
+Source-repository head
+  type:     git
+  location: git://github.com/ppetr/tie-knot.git
+
+Library
+  Build-Depends:     base == 4.*, fixpoint >= 0.1.1 && < 2, containers >= 0.4, mtl >= 2
+  Exposed-Modules:   Data.Knot
+  hs-source-dirs:    src
+--  ghc-options:       -O2