title: How do find identical pairs in Collection?
body: <p>If I have Collection of Set. And I must find identical pairs in Collection, 
  i.e.:</p>
  
  <p>Collection:</p>
  
  <ul>
  <li>Set {Object_A, Object_B, Object_C} </li>
  <li>Set {Object_A, Object_B, Object_F}</li>
  </ul>
  
  <p>How do find pair: Object_A-Object_B in Collection> ?
  What Java library can be used for this purpose?</p>