<p>Tool 1: Plugging Holes</p>
<p><strong>Note</strong>: about 46 minutes and 30 seconds into the example, he uses the example -1, -1, -1, -1, -1, -1, -1, -1 (amongst others). This is invalid because each element must be distinct in a set, so the above example is just {-1}, which has a length of 1, not 8 as the question says.</p>
