/span></span>
<span></span>
<span><span class="co"># Optional argument, if used, must be named. NULL yields the default columns.</span></span>
<span><span class="va">z</span> <span class="op">&lt;-</span> <span class="fu"><a href="../reference/select_required.html">select_required</a></span><span class="op">(</span><span class="va">term</span>, select_add <span class="op">=</span> <span class="cn">NULL</span><span class="op">)</span></span>
<span></span>
<span><span class="co"># Demonstrate equivalence</spa