2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/148722Greiter claimed erroneously that the pi-excitation of the Hubbard model has an energy of the order of U. This mistake originates from a inconsistent treatment of the two particle Hartree energy and the Hartee correction to the chemical potential. In any self-consistent calculations, these two contributions cancel exactly, as shown by Kohn, Luttinger and Ward. We also show that his interpretation of the finite-size studies is inconsistent.3 pages, Latex2eSuperconductivitytext