SEARCH Articles Figures Tables A Generalized Perturbation Theory Brillouin-Wigner perturbation theory generalized Fourth-order, generally perturbation theory General theory Generalized perturbation theory accuracy Generalized perturbation theory formulations Generalized perturbation theory homogeneous systems Generalized perturbation theory versions Generalized theory Many-body perturbation theory general structure Perturbation theory, general methods Perturbation theory, general methods for two-group model