er">b</span>  <span class="special">|</span>                      <span class="identifier">M1</span> <span class="identifier">M3</span>
                                   <span class="identifier">m</span>  <span class="special">|</span> <span class="identifier">m</span> <span class="identifier">m</span> <span class="identifier">m</span> <span class="identifier">m</span>            <span class="identifier">p</span>  <span class="special">|</span>                      <span class="identifier">M1</span> <span 