We saw an example of a state diagram with an infinite state space (Conway's game of life).
We covered sections 20.1 to 20.5, i.e. defining countability and showing that certain example sets are countable. We looked at examples of countable sets, esp. why the set of strings on a finite alphabet is countable. We also saw Cantor's diagonalization proof that P(N) is uncountable, which can be tweaked slightly to show that several other sets (e.g. real numbers, functions from N to {0,1}) are uncountable.