2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/129530Let X be a topological space. The closure of Δ= {(x, x) : x \in X} in X \times X is a symmetric relation on X. We characterise those equivalence relations on an infinite set that arise as the closure of the diagonal with respect to a T_1-topology.8 pagesGeneral TopologyLogic54A99; 04A05text