8.5-8.6, due on February 22

1. 8.5 doesn't seem too bad, kind of just a review of old material, but showing how it is an equivalence relation. 8.6 had me totally lost, though. There were so many new terms, like residence classes, closed under addition or multiplication, and well-defined. Actually most of it made sense after rereading it, but I'm still not quite sure what a residue class is.

2. I thought it was interesting to read that I will see congruence modulo n again, because I had never heard much about that before taking this class, and now it turns out it is some important mathematical concept! Strange.