1.  Object Oriented Programming: An Evolutionary Approach. (2nd ed.)
	Brad J. Cox, Andrew J. Novobilski
	Addison-Wesley Publishing Company, Reading,
	Massachusetts, 1986,1991. ISBN: 0-201-54834-8.
    
    (Spanish: ISBN 0-201-60112-5 Japanese: ISBN 4-8101-8046-8)

2.  An Introduction to Object-Oriented Programming.
        Timothy Budd
	Addison-Wesley Publishing Company, Reading,
	Massachusetts, 1991.  ISBN 0-201-54709-0.

   2nd Edition 1997

3.  Objective-C: Object Oriented Programming Techniques
	Lewis J. Pinson, Richard S. Wiener
	Addison-Wesley Publishing Company, Reading,
	Massachusetts, 1991. ISBN 0-201-50828-1.