<span class="n">key</span> <span class="p">:</span> <span class="n">E_map</span><span class="p">[</span><span class="n">key</span><span class="p">][</span><span class="mi">0</span><span class="p">]</span> <span class="k">for</span> <span class="n">key</span> <span class="ow">in</span> <span class="n">E_map</span><span class="p">}</span>
        
        <span class="n">M_n</span> <span class="o">=</span> <span class="n">M_n</span><span class="o">.</span><span class="n">to_mapper</span><span class="p">(</spa