If a piece of text has a hotlink to this page, then it indicates that it has been altered fairly recently in some possibly significant way and you should check that any paper copies or notes you have are up-to-date.
I will occasionally make errors, and there are sometimes typographical errors in these pages. I will correct the pages as I find errors, but I am not going to list all such corrections. That would take too much time. Hence this page. Once a correction has been in place for a while the hotlink to here will be removed.