Precondition:</b> <tt>n &lt; this-&gt;size()</tt>.<br />
 <b>Effects:</b> Sets bit <tt>n</tt> if <tt>val</tt> is
<tt>true</tt>, and clears bit <tt>n</tt> if <tt>val</tt> is
<tt>false</tt>. <br />
 <b>Returns:</b> <tt>true</tt> if the previous state of bit
<tt>n</tt> was set and <tt>false</tt> is bit <tt>n</tt> is 0.

<hr />
<pre>
reference <a id="bracket">operator[]</a>(size_type n)
</pre>

<b>Precondition:</b> <tt>n &lt; this-&gt;size()</tt>.<br />
 <b>Returns:</b> a <tt>reference</tt> to bit <tt>n</tt>. N