array dimensionality <span class="math inline">\(K &gt; 0\)</span>, then <code>e[i]</code>
has array dimensionality <span class="math inline">\(K-1\)</span> and the same primitive implementation
type as <code>e</code>,</p></li>
<li><p>if <code>e</code> has implementation type <code>vector</code> or <code>row_vector</code> of array
dimensionality 0, then <code>e[i]</code> has implementation type <code>real</code>, and</p></li>
<li><p>if <code>e</code> has implementation type <code>matrix</code>, then <code>e