Seems to be down, here's Google's cache<p><a href="http://webcache.googleusercontent.com/search?q=cache:SHt7f6BhFjIJ:norvig.com/21-days.html+&cd=2&hl=en&ct=clnk&gl=tr&client=ubuntu" rel="nofollow">http://webcache.googleusercontent.com/search?q=cache:SHt7f6B...</a>
Needs a [1998] in the title:
<a href="https://web.archive.org/web/19980206223800/http://www.norvig.com/21-days.html" rel="nofollow">https://web.archive.org/web/19980206223800/http://www.norvig...</a>