Update my answer to Exercise 2.80.

Modified are the following 2 files:

	Exercise_2.80.pdf
	Exercise_2.80.tm

Also, I've added the following 2 files:

	Exercise_2.80.scm
	Test_of_Exercise_2.80.scm

Thank you!
							Lawrence R. Amlord
							   Aug 12th, 2013
							   Xi'an, China