Add my answer to Exercise 4.19.

Included are the following 2 files:

	Exercise_4.19.pdf
	Exercise_4.19.tm

Thank you!
							Lawrence X. Amlord
							  Feb. 11th, 2014
							  Fuzhou, China
Add my answer to Exercise 4.20.

Included are the following 2 files:

	Exercise_4.20.pdf
	Exercise_4.20.tm

Thank you!
							Lawrence X. Amlord
							  Feb 12th, 2014
							  Fuzhou, China
Add my answer to Exercise 4.21.

Included are the following 3 files:

	Exercise_4.21.pdf
	Exercise_4.21.scm
	Exercise_4.21.tm

Thank you!
							Lawrence X. Amlord
							  Feb 13th, 2014
							  Fuzhou, China
Add the code in Section 4.1.7.

Included is the following file:

	4.1.7_Seperating_Syntatic_Analysis_from_Execution.scm

Thank you!
							Lawrence X. Amlord
							  Feb 14th, 2014
							  Fuzhou, China
Metacircular Evaluator (with syntactic analysis seperated from execution).

Included are the following 2 files:

	Metacircular_Evaluator_2e.scm
	Test_fo_Metacircular_Evaluator_2e.scm

Thank you!
							Lawrence X. Amlord
							  Feb 14th, 2014
							  Fuzhou, China