2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/161199We show that for rational surface singularities with odd determinant the mu-bar invariant defined by W. Neumann is an obstruction for the link of the singularity to bound a rational homology 4-ball. We identify the mu-bar invariant with the corresponding correction term in Heegaard Floer theory.12 pages, minor mistakes correctedGeometric Topologytext