2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/30347The resolution of a decades-old open problem is described: polygonal chains cannot lock in the plane.4 pages, 2 figures. To appear in SIGACT News and in Int. J. Comp. Geom. ApplComputational GeometryDiscrete MathematicsF.2.2text