  Some rigorous conclusions of the Hubbard model, Kondo lattice model and
periodic Anderson model at finite temperature are acquired employing the
fluctuation-dissipation theorem and particle-hole transform. The main
conclusion states that for the three models, the expectation value of ${\bf
\tilde{S}}^2-{\bf \tilde{S}}^2_z$ will be of order $N_{\Lambda}$ at any finite
temperature.
