title: How to only match letters that occur more than once in a string, using regex?
body: <p>I am trying to only match letters that appear more than once(twice or more) in a string , using regex for ruby. I came up with the regular expression below but it does not seem to work. I'd appreciate if someone could explain why my regex does not work and tell me how it should be in order for it to work.</p>
  
  <pre><code>/[a-z]{2,}/
  </code></pre>