                    <span class="identifier">distance</span><span class="special">(</span><span class="identifier">a</span><span class="special">,</span><span class="identifier">b</span><span class="special">)</span>
                    <span class="special">:</span> <span class="special">-</span><span class="identifier">distance</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span><span class="identifier">a</span><span class="special">)</span></code>
          