Lecture notes updated

The lecture notes have been updated with the Generalized Wick's Theorem and M?ller--Plesset Perturbation Theory.

Next week, we begin with the electron gas -- the first application of or theory so far to a physical system of interest. Supporting material is Gross/Runge/Heionen Chapter 10 (and also Ch. 5 for the Hamiltonian of a translationally invariant system).