2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/58815Kirby and Lickorish showed that every knot in the 3-sphere is concordant to a prime knot, equivalently, every concordance class contains a prime knot. We prove here that their result can be strengthened: Every knot in the 3-sphere is invertibly concordant to a prime knot. A consequence is that every double concordance class contains a prime knot.6 pages, 3 figures, LaTeX 2eGeometric Topology57M25text