must be itself, and <code>T</code> cannot be an interface.
</p>

<pre>
type MyInt int

interface {
	~[]byte  // the underlying type of []byte is itself
	~MyInt   // illegal: the underlying type of MyInt is not MyInt
	~error   // illegal: error is an interface
}
</pre>

<p>
Union elements denote unions of type sets:
</p>

<pre>