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Anyone have any suggestions for a good write-up on Countability (from an intro to set theory perspective)?

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I don't get the question. – Asaf Karagila Sep 20 '12 at 6:44
@ Asaf - I'm helping out in an undergraduate course in Number Theory and am looking for a good introductory write-up on Countability to give to the students as background reading. Obviously related topics would include Countability of the Rationals, but it's really just for them to get a feel of what Countability (from a Set Theory perspective) is about. Thanks for asking me to clarify. – Conan Wong Sep 20 '12 at 17:21
Are there any other possible perspectives? – Henning Makholm Sep 20 '12 at 20:46
Simply put, a set is countable if and only if it can be put into one-to-one correspondence with the natural numbers or a subset thereof. Now it is perhaps counterintuitive that the rationals are countable, but that can be proven (zig-zag pattern on table of rationals) easily enough. – Justin Benfield Apr 19 at 7:39

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