title: COBOL display all duplicates from a file
body: <p>I have a file which includes a list of different names. Some of some show up twice or more.</p>
  
  <p>I want to display all artists which show up in this list twice or more.</p>
  
  <p>How do I proceed?</p>
  
  <p>Thanks in advance,</p>
  
  <p>Sloan</p>