        <span class="k">raise</span> <span class="ne">ValueError</span>
        <span class="n">suc</span><span class="o">.</span><span class="n">left</span> <span class="o">=</span> <span
            class="n">node</span>
        <span class="n">suc</span><span class="o">.</span><span class="n">pred</span> <span class="o">=</span> <span
            class="n">node</span>
        <span class="n">where</span><span class="o">.</span><span class="n">suc</span> <span class="o">=</span> <span
            class="n