.
        </p>

        <p>
        You need to make two changes to <code>RegexExample.java</code>
        to correctly handle invalid user input.  At the top of the file, add</p>
        <pre>
import org.checkerframework.checker.regex.RegexUtil;
</pre>
        <p>
        After variable <code>regex</code> is defined but before it is
        used (that is, before <code>Pattern pat = Pattern.compile(regex);</code>), add</p>
<pre>
    if (!RegexUtil.isRegex(regex, 1)) {
        System.out.println("Input is no