ion type. <var>Field-names</var>
 must be a list of symbols.  It identifies the fields of the conditions associated with the condition type.</p>
<p><var>Field-names</var>
 must be disjoint from the field names of <var>parent</var>
 and its ancestors.</p>
</dd>
<dt><code>(condition-type? </code><var>thing</var><code>)</code></dt>
<dd><p><code>Condition-type?</code>
 is a predicate for condition types: it returns <code>#t</code>
 if <var>thing</var>
 is a condition type, and <code>#f</code>
 otherwise</p>
</d