PREFACE some equations the notation h.c.appears.This differs from the usual perators to which it is applied.So of AB is AtBt e的T0 xii PREFACE In some equations the notation h.c. appears. This differs from the usual h.c. in that h.c. preserves the order of operators to which it is applied. So the h.c. of AB is B†A† while the h.c. of AB is A†B†. We do not follow the convention of some textbooks in which e stands for the absolute value of the electron charge; we use e = −1.602 × 10−19 C