 class="op">(</span><span class="fu">DAG</span><span class="op">(</span><span class="va">A</span><span class="op">~</span><span class="va">B</span><span class="op">+</span><span class="va">C</span>, <span class="va">D</span><span class="op">~</span><span class="va">D</span><span class="op">)</span><span class="op">)</span></span></span>
<span class="r-plt img"><img src="DAG-3.png" alt="" width="700" height="433"></span>
</code></pre></div>
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