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Why is the set of Rational numbers ,$\mathbb Q$, a countably finite set?
I think that - if we assign $n$ to a rational number, and $n+1$ to another rational number, Then I can surely find a rational number in between these two, which is not accounted for.
I using the definition - If a set is countably infinite, then each element of the set can be mapped to the set of natural numbers.
Another question - Is the cardinal product of countably infinite set of countably infinite sets uncountable or countable?