ABSTRACT
We cheated four times in the last three chapters,* stating (and sometimes motivating) a result but postponing its proof. Those results were:
The formula for decay rates in terms of S-matrix elements, Eq. (4.86).
The master formula for S-matrix elements in terms of Feynman diagrams, Eq. (4.103).
The Ward identity, Eq. (5.79).
The ad hoc subtraction to remove the ultraviolet divergence in the vertex-correction diagram, Eq. (6.55).
