c</a></code>.

<pre>
: (off Sum)
-> NIL
: (accu 'Sum 'a 1)
-> (a . 1)
: (accu 'Sum 'a 5)
-> 6
: (accu 'Sum 22 100)
-> NIL
: Sum
-> ((22 . 100) (a . 6))
</pre></dd>

<dt><a id="acquire"><code>(acquire 'sym) -> flg</code></a></dt>
<dd>Tries to acquire the mutex represented by the file <code>sym</code>, by
obtaining an exclusive lock on that file with <code><a
href="refC.html#ctl">ctl</a></code>, and then trying to write the PID of the
current process into that file. It fails if the file already holds the PID 