This submission has greatly benefitted by reviews from J.M. Brenan, C.J. Capobianco, T. Elliott, G.A. Gaetani, J. Longhi, and E.B. Watson. Unofficial reviews by A. Borisov, N.L. Chabot, B.Z. Hanson, S.W. Jones, D.J. Malvin, A.H. Treiman, and D. Walker have also been extremely helpful. The editorial guidance of J. Blichert-Toft has been critical. I also thank the many friends and colleagues who have guided and abetted me in these endeavours.