Note to users. If you're seeing this message, it means that your browser cannot find this page's style/presentation instructions -- or possibly that you are using a browser that does not support current Web standards. Find out more about why this message is appearing, and what you can do to make your experience of our site the best it can be.
The Table of Contents for the issue of 31 January 1992 (p.508) incorrectly listed a letter by J. Bello as appearing inthe Letters section beginning on page 514. The letter appearedin the issue of 14 February on page 784.