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# quick question! watch

1. How do we show that the set

(P, Q, R, P1, Q1, R1, P2, Q2, R2..)
is countable?
(where the numbers are subscripts)

I guess I need to find a one-one mapping onto natural numbers, but how? there are three sequences, so can't use even and odd numbers..
2. If you really want to use even-odd numbers you could create a countable set containing the P's and Q's and then combine that with the R's.

But if even/odd numbers combine two sequences, how would you combine three?

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Updated: January 24, 2010
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