  The results of G. Su and M. Suzuki [Phys. Rev. B 54, 8291 (1996); ibidem 57,
13367 (1998)] for the spin and pseudo-spin symmetry properties of the Hubbard
model are reexamined. We point out that the exact relations they have found are
valid down to zero temperature and that their solutions for both spin and
pseudo-spin correlation functions are incorrect.

Strongly Correlated Electrons