title: How do you check if two regex's describe the same pattern?
body: <p>Sometimes you may come up with two different regex's for one task. I wonder how you check if two regex's describe the same pattern?</p>
  
  <ul>
  <li><p>Are there some algorithms for that checking?</p></li>
  <li><p>Are there some (online) tools for that checking?</p></li>
  </ul>
  
  <p>For example, I have two regex's here <a href="https://stackoverflow.com/q/24131784/156458">Can we rewrite lookbehind in terms of the if-then-else?</a>, I would like to know if they are the same.</p>
  
  <p>Thanks.</p>