ttribute, you can use the optional operator (see <a class="link" href="optional.html" title="Optional Generator (-a)">Optional
              (unary <code class="computeroutput"><span class="special">-</span></code>)</a>):
            </p>
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<pre class="programlisting"><span class="special">-(</span><span class="identifier">a</span> <span class="special">%</span> <span class="identifier">b</span><span class="special">)</span></pre>
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            </p>
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              which will succeed even if the 