"op">(</span><span class="va">x</span><span class="op">)</span> <span class="op">{</span></span></span>
<span class="r-in"><span>  <span class="va">x</span></span></span>
<span class="r-in"><span><span class="op">}</span>, add_notation <span class="op">=</span> <span class="cn">TRUE</span><span class="op">)</span></span></span>
<span class="r-in"><span><span class="co"># the first element is the entire tree</span></span></span>
<span class="r-in"><span><span class="co"># after FUN was applied to its root el