  Greiter 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.

Superconductivity