As I noted just above, we're already half way through J9.6, which is
mostly the review of spherical bessel, neumann, and hankel functions
that we have just had. The remainder is a lightning review of scalar
spherical harmonics. Since we're about to *generalize* that
concept, we'll quickly go over the high parts.

- Angular momentum and spherical harmonics
- Magnetic and Electric Multipoles Revisited
- Vector Spherical Harmonics and Multipoles

Robert G. Brown 2017-07-11