Notes about the Spring 2022 eTextbook
(as defined by config/PIFLAS22):

* Using Background/MathProof instead of PIFLA/MathProof, since this
  topic is not central enough to justify the effort of doing the PI
  Frames, and they need some work to be ready.

* There are multiple exercise sets for various topics. Will always use
  Set 1 for this semester.

* Will skip the Minimization exercises (MinimizationEx.rst), since
  they need work to be ready.

* RegularGrammars.rst has a number of framesets that were added more
  recently. For Spring 2022, I am going back to something similar to
  what I had originally used, implemented in RegGrammarShort. This
  removes the new framesets about conversion to a left-linear grammar
  and to/from RegEx. None of this is in Linz. The left-linear
  conversion is just vaguely outlined in Linz, and this new slideshow
  is not so clear. And the RegEx stuff seems unnecessary
  detail. Finally, the new frameset for "Something to Think About" is
  not really a good explanation. So I am going back to the original
  prose teaser.

* DFAproperties.rst contains some rough notes originally from Susan
  that (badly) "proves" (through use of converted machine examples on
  a couple sample languages) that two odd properties are closed for
  regular languages. Will skip this. It has been carried through from
  my original book, but I don't think that anyone ever paid it much
  attention. So, will just drop it for S22.

* Will skip the Parsing chapter. This is all prose sketch notes
  anyway.