an><span class="mi">3</span><span class="p">)</span><span class="o">*</span><span class="n">b</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span>
    <span class="n">cross</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span> <span class="o">=</span> <span class="n">a</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span><span class="o">*</span><span class="n">b</span><span class="p">(</span><span class="mi">1</span><span class="