  The Double-Correlated phase in HTSC, and its treatment by field perturbation
theory, is established. In particular, we define the ground state, the
quasi-particle excitations, and construct an appropriate field. We also derive
the unperturbed Hamiltonian, and the propagators for the unperturbed state.
Then we discuss the perturbation Hamiltonian, and show that the Hartree diagram
is significant for both the pseudogap and the superconductive order parameter,
and suggest that it yields the major contribution to these parameters.
