Update my answer to Exercise 4.6.

Modified is the follwoing file:

	Exercise_4.6.scm

Thank you!
							Lawrence X. Amlord
							  Jan 17th, 2013
							  Fuzhou, China
Add my answer to Exercise 4.7.

Included are the following 3 files:

	Exercise_4.7.pdf
	Exercise_4.7.scm
	Exercise_4.7.tm

Thank you!
							Lawrence X. Amlord
							  Jan 17th, 2014
							  Fuzhou, China
Add my answer to Exercise 4.8.

Included is the following file:

	Exercise_4.8.scm

Thank you!
							Lawrence X. Amlord
							  Jan 18th, 2014
							  Fuzhou, China