  The competition between singlet and triplet superconductivity is examined in
consideration of correlations on an extended Hubbard model. It is shown that
the triplet superconductivity may not be included in the common Hubbard model
since the strong correlation favors the singlet superconductivity, and thus the
triplet superconductivity should be induced by the electron-phonon interaction
and the ferromagnetic exchange interaction. We also present a superconducting
qualification with which magnetism is unbeneficial to superconductivity.
