span class="constructor">Invalid_argument</span> <span class="string">"Array.sub"</span></code> if <code class="code">start</code> and <code class="code">len</code> do not
   designate a valid subarray of <code class="code">a</code>; that is, if
   <code class="code">start &lt; 0</code>, or <code class="code">len &lt; 0</code>, or <code class="code">start + len &gt; <span class="constructor">Array</span>.length a</code>.<br>
</p></div>

<pre><span id="VALcopy"><span class="keyword">val</span> copy</span> : 