I need some exercises about functions in general to make sure that I understand it, in a book or a material book. Concepts like function in general (the definition of function), concepts like one-to-one, onto and closure.

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I don't think this qualifies neither as a question nor as something we do here. Why not to use google? –  DonAntonio Sep 22 '12 at 8:50
@DonAntonio: We have had this kind of question before, be sure that I know enough about Google and the fact that I can use it. –  Gigili Sep 22 '12 at 11:33
@WillHunting: I think everybody knows that. If you could name some of them, it'd be more helpful. –  Gigili Sep 22 '12 at 12:12
+1 to make yours here fresh. :) –  B. S. Dec 11 '12 at 1:06

See the section on functions in the first chapter of Fundamentals of Abstract Algebra by Malik, Mordeson and Sen for numerous exercises.

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Yet another nice recommendation! –  amWhy Nov 27 '12 at 0:05