出典:Wikipedia
出典:『Wikipedia』 (2011/06/20 18:34 UTC 版)
In mathematics, a countable set is a set with the same cardinality (number of elements) as some subset of the set of natural numbers. A set that is not countable is called uncountable. The term was originated by Georg Cantor. The elements of a countable set can be counted one at a time—although the counting may never finish, every element of the set will eventually be associated with a natural number.