diff --git a/compare-type.cabal b/compare-type.cabal
--- a/compare-type.cabal
+++ b/compare-type.cabal
@@ -1,6 +1,6 @@
 name: compare-type
 category: Dependent Types
-version: 0.1
+version: 0.1.1
 license: BSD3
 license-file: LICENSE
 cabal-version: >= 1.10
@@ -10,10 +10,10 @@
 stability: provisional
 homepage: https://github.com/Kinokkory/compare-type
 bug-reports: https://github.com/Kinokkory/compare-type/issues
-copyright: (c) Yusuke Matsushita 2014
+copyright: (c) Yusuke Matsushita 2015
 synopsis: compare types of any kinds in haskell
 description:
-    Compare types of any kinds in Haskell.
+    Compare two types of any (possibly different) kinds in Haskell.
     .
     More information can be found in the <http://hackage.haskell.org/package/compare-type hackage's haddock> or the <http://kinokkory.github.io/compare-type/ updated haddock>.
 
@@ -33,6 +33,6 @@
         TypeFamilies,
         UndecidableInstances
     build-depends:
-        base ==4.*
+        base >= 4.7 && < 5
     exposed-modules: Type.Compare
     ghc-options: -Wall
diff --git a/src/Type/Compare.hs b/src/Type/Compare.hs
--- a/src/Type/Compare.hs
+++ b/src/Type/Compare.hs
@@ -4,10 +4,27 @@
     TypeFamilies,
     UndecidableInstances #-}
 
+--------------------------------------------------------------------------------
+-- |
+-- Module: Type.Compare
+-- Copyright: (c) Yusuke Matsushita 2015
+-- License: BSD3
+-- Maintainer: Yusuke Matsushita
+-- Stability: provisional
+-- Portability: portable
+--
+-- Compare two types of any (possibly different) kinds.
+--------------------------------------------------------------------------------
+
 module Type.Compare (
-    -- * Comparison
-    Compare, LargestK(Largest), SmallestK(Smallest), CompareUser,
-    OrdCase, CompareCase, type (<!), type (>=!), type (>!), type (<=!), Max, Min
+    -- * Base
+    Compare,
+    LargestK(Largest), SmallestK(Smallest),
+    CompareUser,
+    -- * Utility
+    OrdCase, CompareCase,
+    type (<!), type (>=!), type (>!), type (<=!),
+    Max, Min
   ) where
 
 import Data.Ord
@@ -24,8 +41,12 @@
 -- | The smallest type (and kind) on 'Compare'.
 data SmallestK = Smallest
 
--- | Compare two types.
+-- | Compare two types of any (possibly different) kinds.
+-- Since `Compare` itself is a closed type family, add instances to `CompareUser` if you want to compare other types.
 type family Compare (a :: k) (b :: k') :: Ordering where
+
+  Compare (Down a) (Down b) = Compare b a
+
   Compare Largest Largest = EQ
   Compare _' Largest = LT
   Compare Largest _' = GT
@@ -33,8 +54,6 @@
   Compare _' Smallest = GT
   Compare Smallest _' = LT
 
-  Compare (Down a) (Down b) = Compare b a
-
   Compare False False = EQ
   Compare False True = LT
   Compare True False = GT
@@ -93,7 +112,7 @@
 
   Compare a b = CompareUser a b
 
--- | Compare two types. Users can add instances.
+-- | Compare two types, of any kinds, which are not compared within `Compare`. Users can add instances.
 type family CompareUser (a :: k) (b :: k') :: Ordering
 
 type family OrdCase (o :: Ordering) (x :: l1) (y :: l2) (z :: l3) :: l where