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Illustration of how the PC algorithm works. (A) Original true causal graph. (B) PC starts with a fully-connected undirected graph. (C) The X − Y edge is removed because X ⫫ Y. (D) The X − W and Y − W edges are removed because X ⫫ W |Z and Y ⫫ W |Z. (E) After finding v-structures. (F) After orientation propagation.
