Add my answer to Exercise 4.17.

Included are the following 2 files:

	Exercise_4.17.pdf
	Exercise_4.17.tm

Thank you!
							Lawrence X. Amlord
							  Feb 10th, 2014
							  Fuzhou, China
Add my answer to Exercise 4.18.

Included are the following 2 files:

	Exercise_4.18.pdf
	Exercise_4.18.tm

Thank you!
							Lawrence X. Amlord
							  Feb 11th, 2014
							  Fuzhou, China