Figure 1: (a) The electron band of a symmetric Friedel impurity with the -resonance at the Fermi level. (b) The effective band (density of states) after turning on the Coulomb repulsion and setting . The Friedel resonances are transformed into broad Hubbard resonances, roughly positioned at and , far away from the Fermi level and an extremely narrow Kondo resonance at the Fermi level.