definition of an interface's type set as follows:
</p>

<ul>
	<li>The type set of the empty interface is the set of all non-interface types.
	</li>

	<li>The type set of a non-empty interface is the intersection of the type sets
		of its interface elements.
	</li>

	<li>The type set of a method specification is the set of all non-interface types