diff --git a/groups.cabal b/groups.cabal
--- a/groups.cabal
+++ b/groups.cabal
@@ -1,5 +1,5 @@
 name:                groups
-version:             0.1.0.1
+version:             0.2.0.0
 synopsis:            Haskell 98 groups
 description:         
   Haskell 98 groups. A group is a monoid with invertibility.
diff --git a/src/Data/Group.hs b/src/Data/Group.hs
--- a/src/Data/Group.hs
+++ b/src/Data/Group.hs
@@ -4,7 +4,8 @@
 
 -- |A 'Group' is a 'Monoid' plus a function, 'invert', such that: 
 --
--- @a <> invert a == mempty@
+-- @a \<> invert a == mempty@
+-- @invert a \<> a == mempty@
 class Monoid m => Group m where
   invert :: m -> m
   
@@ -22,7 +23,10 @@
 instance Group a => Group (Dual a) where
   invert = Dual . invert . getDual
   {-# INLINE invert #-}
-  
+
+instance Group b => Group (a -> b) where
+  invert f = invert . f
+
 instance (Group a, Group b) => Group (a, b) where
   invert (a, b) = (invert a, invert b)