countable set

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countable set A set that, in some sense, is no larger than the set of natural numbers. The elements of the set can be put into order and counted. Such a set is either finite or denumerable; the elements of a denumerable set can be placed in a one-to-one correspondence with the set of natural numbers. The set of rational numbers can be shown to be countable but the set of real numbers is not countable.

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