Add answer to Exercise 1.13

Included are the following 2 files:

	Exercise_1.13.pdf
	Exercise_1.13.tm

Exercise 1.13 does challenges one's mathematical maturity, especially the
inductionn.

I'm not sure that my proof here is rigorous enough. If you have a better
approach, please contact me through email put in my GitHub account!

Thank you!
							Lawrence R. Amlord
							   Apr. 19, 2013
							   Xi'an, China