title: Find subsequences of strings within strings
body: <p>I want to make a function which checks a string for occurrences of other strings within them.<br>
  However, the sub-strings which are being checked may be interrupted within the main string by other letters.  </p>
  
  <p>For instance:  </p>
  
  <pre><code>a = 'abcde'
  b = 'ace'
  c = 'acb'
  </code></pre>
  
  <p>The function in question should return as <code>b</code> being in <code>a</code>, but not <code>c</code>.  </p>
  
  <p>I've tried <code>set(a)</code>. intersection(set(b)) already, and my problem with that is that it returns <code>c</code> as being in <code>a</code>.  </p>