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The cluster-expansion approach to the correlation problem. pioneered by Coester. Kummel, Cizek and Paldus. is extended to calculation of static and dynamic propcrtics of many-fcrmion systems. Linear. inhomogeneous equations are obtaincd for properties of any order. A time-dependent formulation gives frequency-dependent properties. yielding excitation energies. transition probabilities, and (possibly) life times reminiscent of Green's function methods.