diff --git a/singleton/src/main/java/com/iluwatar/EnumIvoryTower.java b/singleton/src/main/java/com/iluwatar/EnumIvoryTower.java
index e9c3dc4dc..a9858d99e 100644
--- a/singleton/src/main/java/com/iluwatar/EnumIvoryTower.java
+++ b/singleton/src/main/java/com/iluwatar/EnumIvoryTower.java
@@ -3,9 +3,11 @@ package com.iluwatar;
 /**
  *
  * Enum Singleton class.
+ * Effective Java 2nd Edition (Joshua Bloch) p. 18
  *
  */
 public enum EnumIvoryTower {
+	
     INSTANCE;
 
     @Override