 for deep-copying Proto expression trees. When a tree is deep-copied, all internal
            nodes and terminals held by reference are instead held by value.</p>
<div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody><tr>
<td><p><span class="term">Notes:</span></p></td>
<td>
<p>
            Terminals of reference-to-function type are left unchanged.
          </p>
<p>
            Equivalent to <code class="computeroutpu