In this appendix some of the angular momentum theory needed for the construction of configuration state functions is summarized. Also, spherical tensor operators and reduced matrix elements are discussed briefly. For a more comprehensive treatment we refer the reader to Silver (1976). Not discussed here are the use of the creation operator for constructing anti-symmetrized states nor the expression of sums of operators fi acting on the single electron i, or sums of operators gij operating on the pair of electrons i and j, in terms of creation and annihilation operators, concepts that are part of second quantization. Together with the notion of quasispin, this approach has been shown to lead to faster methods for the evaluation of matrix elements (Gaigalas and Rudzikas 1996). For a review of second quantization, see Judd (1996).