=</span> <span class="cn">TRUE</span><span class="op">)</span></span></span>
<span class="r-in"><span>  <span class="co"># example</span></span></span>
<span class="r-in"><span>  <span class="va">set</span> <span class="op">&lt;-</span> <span class="fu"><a href="https://rdrr.io/r/base/c.html" class="external-link">c</a></span><span class="op">(</span><span class="st">"1"</span>, <span class="st">"2"</span><span class="op">)</span></span></span>
<span class="r-in"><span>  <span class="va">op_tree</span> <spa