<p>
If <code>a</code> is not a map:
</p>
<ul>
	<li>the index <code>x</code> must be of integer type or an untyped constant</li>
	<li>a constant index must be non-negative and
	    <a href="#Representability">representable</a> by a value of type <code>int</code></li>
	<li>a constant index that is untyped is given type <code>int</code></li>
	<li>the index <code>x</code> is <i>in range</i> if <code>0 &lt;= x &lt; len(a)</code>,