This work was completed in the summer of 1991 when the first-listed author enjoyed a “study-grant” from the Deutscher Akademischer
Austauschdients (=“DAAD”) of the Federal Republic of Germany and, subsequently, generous hospitality and support from the
Technische Hochschule Darmstadt. He is pleased to thank these institutions, as well as the National University of Singapore
for hospitality while the manuscript was prepared for publication (summer, 1992)