ion that every key and at least one
of every pair of socks will eventually be lost forever, using only the
following vocabulary: ${Key}(x)$, $x$ is a key; ${Sock}(x)$, $x$ is
a sock; ${Pair}(x,y)$, $x$ and $y$ are a pair; ${Now}$, the current
time; ${Before}(t_1,t_2)$, time $t_1$ comes before time $t_2$;
${Lost}(x,t)$, object $x$ is lost at time $t$.
</p>
    </div>
</div>

<p><br /></p>

<div class="card">
    <div class="card-header p-2">
        <a href="ex_27/" class="p-2">Exercise 27 </a>
        <butt