}
</pre>

<p>
Implementation restriction:
A union (with more than one term) cannot contain the
<a href="#Predeclared_identifiers">predeclared identifier</a> <code>comparable</code>
or interfaces that specify methods, or embed <code>comparable</code> or interfaces
that specify methods.
</p>

<p>
Interfaces that are not <a href="#Basic_interfaces">basic</a> may only be used as type