</li>

	<li>The type set of a <i>union</i> of terms
		<code>t<sub>1</sub>|t<sub>2</sub>|…|t<sub>n</sub></code>
		is the union of the type sets of the terms.
	</li>
</ul>

<p>
The quantification "the set of all non-interface types" refers not just to all (non-interface)
types declared in the program at hand, but all possible types in all possible programs, and
hence is infinite.