Minor updates to the text of the lectures

Those who have seen the book version of the web site know that the book follows the text of the lectures. Nevertheless, some minor improvements in the presentation were made during the preparation of the book chapters. As a consequence the book presents some material in a clearer way, and some passages are easier to read in the book than on the web.

In the coming weeks I intend to remedy this and go through the text of the web lectures and associated material to bring them into alignment with the book version. Any changes will be very minor and not change the essence of the text. Amended lectures will be annotated with the date of the last update from now on.