I would like to thank Avinash Sathaye, Birgit Kellner, and Artur Karp for their informative and suggestive responses to my query. With these, my son will have excellent material for answering the assignment question. Please consider this query closed. Thank you. Elliot M. Stern 552 South 48th Street Philadelphia, PA 19143-2029 USA telephone: 215 747 6204