title: How does the google short url works?
body: <p>How can the Google short URL cater for so many URLs in web with just four character, even though alphabets are case sensitive?</p>
  
  <p><a href="http://goo.gl/SUWp" rel="nofollow noreferrer">http://goo.gl/SUWp</a></p>
  
  <p>Say fn(some url)-> four letter for url, how can they suddenly use the same function which gives five letter for url after sometime? How will they know whether it is in four letter or five letter url from url?</p>