2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/229955We prove that the criterion for Markov equivalence provided by Zhao et al. (2005) may involve a set of features of a graph that is exponential in the number of vertices.2 pages, 1 figure, supplement to paper to appear in the Annals of StatisticsMachine Learningtext