diff --git a/fast-arithmetic.cabal b/fast-arithmetic.cabal
--- a/fast-arithmetic.cabal
+++ b/fast-arithmetic.cabal
@@ -1,5 +1,5 @@
 name:                fast-arithmetic
-version:             0.2.2.0
+version:             0.2.2.1
 synopsis:            Fast functions on integers.
 description:         Fast functions for number theory and combinatorics with a high level of safety guaranteed by [ATS](http://www.ats-lang.org/). This package also provides a
                      'Storable' instance for GMP's @mpz@ type.
diff --git a/src/Numeric/Pure.hs b/src/Numeric/Pure.hs
--- a/src/Numeric/Pure.hs
+++ b/src/Numeric/Pure.hs
@@ -31,6 +31,9 @@
 {-# SPECIALIZE hsDoubleFactorial :: Int -> Int #-}
 
 -- | See [here](http://mathworld.wolfram.com/Derangement.html).
+--
+-- > λ:> fmap derangement [0..10] :: [Integer]
+-- > [1,0,1,2,9,44,265,1854,14833,133496,1334961]
 derangement :: (Integral a) => Int -> a
 derangement n = derangements !! n