A2 = A1
)

type (
	B1 string
	B2 B1
	B3 []B1
	B4 B3
)

func f[P any](x P) { … }
</pre>

<p>
The underlying type of <code>string</code>, <code>A1</code>, <code>A2</code>, <code>B1</code>,
and <code>B2</code> is <code>string</code>.
The underlying type of <code>[]B1</code>, <code>B3</code>, and <code>B4</code> is <code>[]B1</code>.