added code from Figures 3.6 and 3.7, and output code, in preparation for adding modifications called-for by Exercise 3.7;
strangely, only one tweak was needed (changing a "list" to a "cons") - I feel like my last attempt at this required more surgery (guess not);
added solutions for Exercise 8;
added solutions to Exercise 9;
I went back to using the "new-paths" function - code looks cleaner this way;