“…There are a variety of expositions on this topic; we select a few aspects of the theory to discuss, based on the author's preferences. The reader can confer with any of the following general references for more details: [21,22,30,32,33,35,36,48,94,95,100,102,184,186,187,206,236,258]. The reader is cautioned that notation in these papers is not particularly consistent between various authors.…”