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  1. I

    Counting infinite sequence of sets

    I'm sorry, >.< but what does NxN mean? is it the symbol for natural number?
  2. I

    Counting infinite sequence of sets

    Denumerable? The set K would be denumberable if there is a bijection ZZ+->K by the way, can you teach me how to read "Bijection ZZ+->K?" ZZ+ is the symbol for all positive integer, -> is the arrow pointing to the set K. and I have trouble understanding what F: NN -> A mean intuitively
  3. I

    Counting infinite sequence of sets

    Let K1, K2, K3, . . . be an infnite sequence of sets, where each set Kn is countable. Prove that the union of all of these sets K = Union from n=1 to infinity, Kn is countable. I tried to start, but I don't even understand the question Need some idea on how to start
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