ABSTRACT
Note that in (9.92) we have included odd as well as
even powers of σ and also arbitrary indices. This has
been done only to remind the reader that there are infinite
varieties of Hamiltonians other than the ones we have been
studying. In all our e a r l ie r discussions we have assumed
complete rotation symmetry except for the magnetic field
h. The effect of anisotropy w ill be our next subject.
