Fixes a typo and a sentence in chapter 8. Diagrams (8) and (9) involve f_ph matrix elements, i.e., they vanish in the canonical HF case.
Fixes a typo and a sentence in chapter 8. Diagrams (8) and (9) involve f_ph matrix elements, i.e., they vanish in the canonical HF case.

ManyBodyPhysics/LectureNotesPhysics,ManyBodyPhysics/LectureNotesPhysics,ManyBodyPhysics/LectureNotesPhysics,ManyBodyPhysics/LectureNotesPhysics