4.2.3, due Sept 11

1) (Difficult) I had trouble understanding what a reduced residue system was and also had a hard time understanding Lemma 2.4.3.4 and Lemma 2.4.3.5.

2) (Reflective) I notice that there were some thrm that didn't quite make sense to me when I first read them, but through reading the proof for the thrm I was actually able to understand what the thrm was saying. For example I was able to do this with Thrm 2.4.3.1.