Sec. 7, 3.1-3.3 Due January 20th

The most difficult thing for me to follow was the books use of a lemma in a proof.  The proof was to veryify for integers that if 5x-7 were odd, then 9x+2 was even.  The lemma used was that if 5x-7 is odd then x is even.  I failed to understand were they pulled x being even from, and how it was known that this would assist in the proof.  Aside from that I found proofs by contrapositive to be interesting.  They made sense and appear to be useful in many cases.