2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/163751The following problem is NP-hard: given a regular expression $E$, decide if $E^*$ is not co-finite.2 pages, working paper; an error in Problem 5 is correctedDiscrete MathematicsComputational ComplexityF.2.2; G.2.1text