ass="identifier">multiset_of</span><span class="special">&lt;</span> <span class="identifier">tagged</span><span class="special">&lt;</span> <span class="keyword">int</span><span class="special">,</span> <span class="identifier">Left</span>  <span class="special">&gt;</span> <span class="special">&gt;,</span>
    <span class="identifier">unordered_set_of</span><span class="special">&lt;</span> <span class="identifier">tagged</span><span class="special">&lt;</span> <span class="keyword">int</span><span class