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diff --git a/Haskell-book/15/orphan-instance/ListyInstances.hs b/Haskell-book/15/orphan-instance/ListyInstances.hs
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+module ListyInstances where
+
+import Data.Monoid
+import Listy
+
+instance Monoid (Listy a) where
+    mempty = Listy []
+    mappend (Listy l) (Listy l') =
+        Listy $ mappend l l'