l.Lock()
	go f()
	l.Lock()
	print(a)
}
</pre>

<p>
is guaranteed to print <code>"hello, world"</code>.
The first call to <code>l.Unlock()</code> (in <code>f</code>) is synchronized
before the second call to <code>l.Lock()</code> (in <code>main</code>) returns,
which is sequenced before the <code>print</code>.
</p>

<p class="rule">

<code>f</code> is a function returning two values,
</p>

<pre>
x, y = f()
</pre>

<p>
assigns the first value to <code>x</code> and the second to <code>y</code>.
In the second form, the number of operands on the left must equal the number
of expressions on the right, each of which must be single-valued, and the
<i>n</i>th expression on the right is assigned to the <i>n</i>th

<code>f</code> is a function returning two values,
</p>

<pre>
x, y = f()
</pre>

<p>
assigns the first value to <code>x</code> and the second to <code>y</code>.
In the second form, the number of operands on the left must equal the number
of expressions on the right, each of which must be single-valued, and the
<i>n</i>th expression on the right is assigned to the <i>n</i>th