Add my answer to Exercise 3.17.

Included are the following 2 files:

	Exercise_3.17.scm
	Test_of_Exercise_3.17.scm

Thank you!
							Lawrence X. Amlord
							  Sept 22nd, 2013
							  Xi'an, China
Add my answer to Exercise 3.18.

Included are the following 2 files:

	Exercise_3.18.scm
	Test_of_Exercise_3.18.scm

Thank you!
							Lawrence X. Amlord
							  Sept 22nd, 2013
							  Xi'an, China
Add my answer to Exercise 3.19.

Included are the following 2 files:

	Exercise_3.19.scm
	Test_of_Exercise_3.19.scm

Thank you!
							Lawrence X. Amlord
							  Sept 22nd, 2013
							  Xi'an, China