In retrospect, the range of topics covered in this monograph, although forming a coherent ensemble, is so extensive that a detailed discussion could easily extend to three or four times the current length. My approach has been to identify the critical issues, summarize the major accomplishments, and to suggest promising avenues for future research. To facilitate this sum mary presentation, I have limited the literature review largely to material published after 1970, extending to material appearing late in 1990. I gratefully acknowledge the advice of many colleagues, particularly the valuable...
In retrospect, the range of topics covered in this monograph, although forming a coherent ensemble, is so extensive that a detailed discussion could e...
