Update my answer to Exercise 1.12.

Modified are the following 3 files:

	Exercise_1.12.pdf
	Exercise_1.12.scm
	Exercise_1.12.tm

Additionally, a new file has been added in:

	Test_of_Exercise_1.12.scm

Thank you!
							Lawrence X. Amlord
							  Nov 10th, 2013
							  Xi'an, China