is, for each adjacent element pair
                <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>, of <code class="computeroutput"><span class="identifier">rng2</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="id