Start Ch.9
Merge pull request #3 from CdLbB/master

Minor typos fixed in chapter 7 sections 1 and 2
Small amount of work for Ch.9
Fix typo in Ch.7
Work on Ch.9
Work on Ch.9
Work on Ch.9
Work on Ch.9
Work on Ch.9
Work on Ch.9
Work on Ch.9
Work on Ch.9
Work on Ch.9
Work on Ch.9
Work on Ch.9
Work on Ch.9
Work on Ch.9
Work on Ch.9
Work on Ch.9
Work on Ch.9