_a</span>: Add a 'a' value defined separately</span>
<span class="r-out co"><span class="r-pr">#&gt;</span> </span>
<span class="r-out co"><span class="r-pr">#&gt;</span> <span style="background-color: #00BBBB;">Usage</span>: add_a(x)</span>
<span class="r-out co"><span class="r-pr">#&gt;</span> </span>
<span class="r-out co"><span class="r-pr">#&gt;</span> <span style="background-color: #00BBBB;">Parameters</span>:</span>
<span class="r-out co"><span class="r-pr">#&gt;</span>   - <span style="text-decorati