Fix an important bug in my answer to Exercise 2.87.

Modified are the following 2 files:

	Exercise_2.87.scm
	Test_of_Exercise_2.87.scm

Thank you!
							Lawrence R. Amlord
							   Aug 21st, 2013
							   Fuzhou, China
Update my answer to Exercise 2.89.

Modified is the following file:

	Exercise_2.89.scm

Additionally, a file of testing has been included:

	Test_of_Exercise_2.89.scm

Thank you!
							Lawrence R. Amlord
							   Aug 22nd, 2013
							   Fuzhou, China
Update my answer to Exercise 2.89.

Modified are the following 4 files:

	Exercise_2.89.pdf
	Exercise_2.89.scm
	Exercise_2.89.tm
	Test_of_Exercise_2.89.scm

Thank you!
							Lawrence R. Amlord
							   Aug 22nd, 2013
							   Fuzhou, China