A coupled spin-fermion model is presented as a two-band model of high-Tc superconductivity. The experimental relevance of the model is discussed. The high-Tc superconductivity is discussed the continuity of the strong coupling superconductivity to the weak coupling region. The attractive interaction of holes seems to exist over a wide range of parameters from weak to strong coupling cases. The small transfer region is useful to understand the pairing mechanism in the relevant strong coupling region. The model includes the effective Hamiltonian of the single-band Hubbard model as a special case.
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