s designed by <code class="computeroutput"><span class="identifier">pred</span></code> such that for all adjacent elements
            <code class="computeroutput"><span class="special">[</span><span class="identifier">x</span><span class="special">,</span><span class="identifier">y</span><span class="special">]</span></code>, <code class="computeroutput"><span class="identifier">pred</span><span class="special">(</span><span class="identifier">y</span><span class="special">,</span><span class="identifier">