public static void mapMystery2(Map m) { 

 Set s = new TreeSet(); 

 for (String key : m.keySet()) { 

 if (!m.get(key).equals(key)) { 

 s.add(m.get(key)); 

 } else { 

 s.remove(m.get(key)); 

 } 

 } 

 System.out.println(s); 

} 

{sheep=wool, house=brick, cast=plaster, wool=wool}
{munchkin=blue, winkie=yellow, corn=yellow, grass=green, emerald=green}
{pumpkin=peach, corn=apple, apple=apple, pie=fruit, peach=peach}
{lab=ipl, lion=cat, terrier=dog, cat=cat, platypus=animal, nyan=cat} How does this work? Can someone explain?