Chapters 2.1, 2.2, 2.4 for lecture on 11 September

1. The hardest part was decrypting the affine cipher. It mostly involved recalling what we read in the previous chapter about solving congruences, so I needed to review it to understand it.

2. It was interesting to see some more hints at solving substitution ciphers besides a character count, such as looking at pairs of letters and looking at general trends in English.