Updated to version 2022-04-30: 03431 (deleted a redundant sentence, fixed an out-of-sync phrase, reworded a few sentences, clarified one footnote)
21916 (removed a broken cross-reference, clarified one sentence, rearranged one paragraph)
22871 (fixed a spelling error)
70833 (deleted one word, and fixed a cross-reference)
74088 (updated/added references, added a footnote, genralized one theorem, changed one word)
77228 (added two new footnotes)
90771 (added a new section about bases, rewrote the section about separability, updated/added some references)
Also: Re-posted all pdf files to change the color of hyperlinks from black to blue, to clarify the fact that the hyperlinks actually do something. Didn't change any version numbers/dates.