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Math Help - proof of countable

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    proof of countable

    Prove that the set {1,2,3}xnatural numbers is countable.
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  2. #2
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    Quote Originally Posted by natewalker205 View Post
    Prove that the set {1,2,3}xnatural numbers is countable.

    Hint:
    if X = \{1,2,3\} \times \mathbb{N}, \text{consider } f:X \to \mathbb{N} defined as f((i,n)) = 3(n-1)+i

    P.S: Though I have tailored this definition for this problem, any cartesian product of countable sets is countable
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