diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
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+Copyright Péter Diviánszky 2008
+
+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 name of Péter Diviánszky nor the names of other
+ 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/Number/Peano/Inf.hs b/Number/Peano/Inf.hs
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+{- |
+Copyright : (c) Peter Divianszky 2008
+Maintainer : divip@aszt.inf.elte.hu
+Stability : experimental
+Portability : portable
+
+Lazy Peano numbers including observable infinity value.
+-}
+module Number.Peano.Inf
+ ( Nat (Zero, Succ)
+ , infinity
+ , isInfinity
+ , (-|)
+ ) where
+
+import Data.Ratio ((%))
+
+-- | Natural numbers and infinity.
+data Nat
+ = Zero
+ | Succ Nat
+ | Inf
+
+-- | Observable infinity value.
+
+infinity :: Nat
+infinity = Inf
+
+-- | True for @(infinity)@, @(5 + 4 * infinity)@ etc. Evaluates to bottom for @(genericLength [1..])@.
+
+isInfinity :: Nat -> Bool
+isInfinity Zero = False
+isInfinity Inf = True
+isInfinity (Succ n) = isInfinity n
+
+instance Eq Nat where
+
+ Zero == Zero = True
+ Succ n == Succ m = n == m
+ Inf == Inf = error "Nat: infinity == infinity"
+ Succ n == Inf = n == Inf
+ Inf == Succ m = Inf == m
+ _ == _ = False
+
+instance Ord Nat where
+
+ Zero `compare` Zero = EQ
+ Zero `compare` _ = LT
+ _ `compare` Zero = GT
+ Succ n `compare` Succ m = n `compare` m
+ Inf `compare` Inf = error "Nat: infinity `compare` infinity"
+ Inf `compare` Succ m = Inf `compare` m
+ Succ n `compare` Inf = n `compare` Inf
+
+ _ < Zero = False
+ Zero < _ = True
+ Succ n < Succ m = n < m
+ Inf < Inf = error "Nat: infinity < infinity"
+ Inf < Succ m = Inf < m
+ Succ n < Inf = n < Inf
+
+ x > y = y < x
+
+ x <= y = not (y < x)
+
+ x >= y = not (x < y)
+
+ Zero `max` x = x
+ x `max` Zero = x
+ Succ n `max` Succ m = Succ (n `max` m)
+ _ `max` _ = Inf
+
+ Zero `min` _ = Zero
+ _ `min` Zero = Zero
+ Succ n `min` Succ m = Succ (n `min` m)
+ Inf `min` m = m
+ n `min` Inf = n
+
+instance Show Nat where
+
+ show Inf = "infinity"
+ show x = show $ toInteger x
+
+-- | Subtraction maximized to 0. For example, @(5 -| 8 == 0)@.
+
+infixl 6 -|
+(-|) :: Nat -> Nat -> Nat
+Inf -| Inf = error "Nat: infinity -| infinity"
+Inf -| _ = Inf
+Succ n -| Succ m = n -| m
+n -| Zero = n
+_ -| _ = Zero
+
+
+instance Num Nat where
+
+ Inf - Inf = error "Nat: infinity - infinity"
+ Inf - _ = Inf
+ Succ n - Succ m = n - m
+ n - Zero = n
+ _ - Inf = error "Nat: n - inifinty"
+ Zero - Succ _ = error "Nat: 0 - succ n"
+
+ Zero + m = m
+ Succ n + m = Succ (n + m)
+ Inf + _ = Inf
+
+ Succ n * m = m + n * m
+ Zero * _ = Zero
+ Inf * _ = Inf
+
+ fromInteger i | i < 0 = error "Nat: fromInteger on negative value."
+ fromInteger i = iterate Succ Zero !! fromInteger i
+
+ abs x = x
+
+ signum Zero = Zero
+ signum _ = Succ Zero
+
+instance Enum Nat where
+
+ toEnum i | i < 0 = error "Nat: toEnum on negative value."
+ toEnum i = iterate Succ Zero !! i
+
+ fromEnum n = f 0 n where
+
+ f i Zero = i
+ f i (Succ m) = i' `seq` f i' m where i' = i+1
+
+instance Real Nat where
+
+ toRational n = fromIntegral n % 1
+
+instance Integral Nat where
+
+ toInteger n = f 0 n where
+
+ f i Zero = i
+ f i (Succ m) = i' `seq` f i' m where i' = i+1
+
+ quotRem _ _ = error "Nat: quotRem not implemented."
+
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/peano-inf.cabal b/peano-inf.cabal
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+++ b/peano-inf.cabal
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+name: peano-inf
+version: 0.1
+synopsis: Lazy Peano numbers including observable infinity value.
+description:
+ Lazy Peano numbers including observable infinity value.
+ .
+ This data type was needed in a graph traversing algorithm.
+ .
+ This data type is ideal for lazy list length computation (the infinite value is not needed in this case).
+ See also
+category: Data
+author: Péter Diviánszky
+maintainer: Péter Diviánszky
+copyright: (c) 2008 by Péter Diviánszky
+license: BSD3
+license-file: LICENSE
+stability: experimental
+build-type: Simple
+cabal-version: >=1.2
+
+library
+ ghc-options: -Wall -fno-warn-overlapping-patterns -fno-warn-incomplete-patterns
+ build-depends:
+ base
+
+ exposed-modules:
+ Number.Peano.Inf
+
+