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<p><span class="math display">\[Y \leftarrow C \rightarrow X\]</span> In this DAG, there is no way for influence to flow from X to Y; the one-way links don’t permit it. We have used water as an analogy for causal influence. For <em>information</em>, we need another analogy. Consider <em>ants</em>.</p>
<p>We will allow the ants to move in only one direction along a link. So in <span class="math inline">\(Y \leftarrow C \rightarrow X\)</span>, ants can move from C to Y. They can also move from C to X. Bu