Project Euler problem number 4
<pre><code>n = 0
for a in xrange(999, 100, -1):
    for b in xrange(a, 100, -1):
        x = a * b
        if x &gt; n:
            s = str(a * b)
            if s == s[::-1]:
                 n = a * b
print n
</code></pre>

<p>I have a question about this solution to <a href="http://projecteuler.net/index.php?section=problems&amp;id=4" rel="nofollow">the problem</a>.
I know it is right but I am wondering why in the <code>xrange(999,100,-1)</code> the <code>-1</code> is there
For the a and b for loops. Please explain. I am new to this :)</p>
