2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/69078We investigate configurations of rational double points with the total Milnor number 21 on supersingular $K3$ surfaces. The complete list of possible configurations is given. As an application, we also give the complete list of extremal (quasi-)elliptic fibrations on supersingular $K3$ surfaces.31 pagesAlgebraic Geometry14J28text