<code>S2</code>, regardless of what other methods
<code>S1</code> and <code>S2</code> may have or share.
</p>

<p>
A type implements any interface comprising any subset of its methods
and may therefore implement several distinct interfaces. For
instance, all types implement the <i>empty interface</i>:
</p>

<pre>
interface{}
</pre>

<p>

observes a synchronizing write-like memory operation <i>w</i>
(that is, if <i>W</i>(<i>r</i>) = <i>w</i>),
then <i>w</i> is synchronized before <i>r</i>.
Informally, the synchronized before relation is a subset of the implied total order
mentioned in the previous paragraph,
limited to the information that <i>W</i> directly observes.
</p>

<p>
The <i>happens before</i> relation is defined as the transitive closure of the

	corresponding method types unify exactly,
	and the method set of one of the interfaces is a subset of
	the method set of the other interface.
</li>
<li>
	Only one type is an interface (but not a type parameter),
	corresponding methods of the two types unify per the element matching mode,
	and the method set of the interface is a subset of
	the method set of the other type.
</li>
<li>