diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,27 @@
+Copyright (c) 2013 Mikhail Vorozhtsov
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without 
+modification, are permitted provided that the following conditions are met:
+
+- Redistributions of source code must retain the above copyright notice, 
+  this list of conditions and the following disclaimer.
+- Redistributions in binary form must reproduce the above copyright 
+  notice, this list of conditions and the following disclaimer in the 
+  documentation and/or other materials provided with the distribution.
+- Neither the names of the copyright owners nor the names of the 
+  contributors may be used to endorse or promote products derived 
+  from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
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/data-checked.cabal b/data-checked.cabal
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+++ b/data-checked.cabal
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+Name: data-checked
+Version: 0.1
+Category: Data
+Stability: experimental
+Synopsis: Type-indexed runtime-checked properties 
+Description:
+  This package provides a (phantom) type-indexed newtype evidence-wrapper for
+  values that are checked to satisfy the property associated with the type. 
+
+Homepage: https://github.com/mvv/data-checked
+Bug-Reports: https://github.com/mvv/data-checked/issues
+
+Author: Mikhail Vorozhtsov <mikhail.vorozhtsov@gmail.com>
+Maintainer: Mikhail Vorozhtsov <mikhail.vorozhtsov@gmail.com>
+Copyright: 2013 Mikhail Vorozhtsov <mikhail.vorozhtsov@gmail.com>
+License: BSD3
+License-File: LICENSE
+
+Cabal-Version: >= 1.6.0
+Build-Type: Simple
+
+Source-Repository head
+  Type: git
+  Location: https://github.com/mvv/data-checked.git
+
+Library
+  Build-Depends:
+    base >= 4 && < 5
+  Hs-Source-Dirs: src
+  GHC-Options: -Wall
+  Exposed-Modules:
+    Data.Checked
+
diff --git a/src/Data/Checked.hs b/src/Data/Checked.hs
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+++ b/src/Data/Checked.hs
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+{-# LANGUAGE UnicodeSyntax #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+
+-- | Type-indexed runtime-checked properties.
+module Data.Checked
+  ( Checked
+  , trustMe
+  , checked
+  , Property(..)
+  , maybeHolds
+  , check
+  ) where
+
+-- | Wrapper-evidence for property /p/.
+newtype Checked p v = Checked v
+
+-- | Use when the property can be deduced without a runtime check.
+trustMe ∷ v → Checked p v
+trustMe = Checked
+{-# INLINE trustMe #-}
+
+-- | Unwrap the checked value.
+checked ∷ Checked p v → v
+checked (Checked v) = v
+{-# INLINE checked #-}
+
+class Property p v where
+  -- | Test if the property holds for the given value.
+  --   The first argument is supposed to be ignored.
+  holds ∷ p → v → Bool
+
+-- | Return 'Just' /v/ if /p/ holds and 'Nothing' overwise.
+maybeHolds ∷ Property p v ⇒ p → v → Maybe v
+maybeHolds p v | holds p v = Just v
+               | otherwise = Nothing
+{-# INLINABLE maybeHolds #-}
+
+-- | Wrap the value if the property holds.
+check ∷ ∀ p v . Property p v ⇒ v → Maybe (Checked p v)
+check v | holds (undefined ∷ p) v = Just (Checked v)
+        | otherwise               = Nothing
+{-# INLINABLE check #-}
+