Find subsequences of strings within strings
<p>I want to make a function which checks a string for occurrences of other strings within them.
However, the substrings 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 b being in a, but not c.</p>

<p>I've tried set(a).intersection(set(b)) already, and my problem with that is that it returns c as being in a.</p>
