Keeping this accurate

Care goes into this material, and even so it carries no promise of being complete, current, or error-free. What is described here can change without this page changing with it.

Linked material

Some links lead to websites operated by others. What those websites publish, and how they treat visitors, is their responsibility and not this one's.

Amendments

Expect this to be revised from time to time. Check this page for the current position.

Reporting an error

Write to [email protected] with any question about what is explained on this website.