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Cardinality is a measure of the size of a set. For finite sets, its cardinality is simply the number of elements in it.
Cardinality is a measure of the size of a [[set theory|set]]. For [[finite]] sets, its cardinality is simply the number of elements in it. In general, two sets have the same cardinality if there is a [[bijection]] between them. That is, the elements of one set can be put into one-to-one correspondence with those of the other.
For example, the set of even numbers, and the set of all multiples of 3 is the same, as they can be put into one-to-one correspondence as follows:
2:3,4:6,6:9,8:12,10:15,..2n:3n...
Both sets are [[countable]], as they have the same cardinality as the set of [[natural number]]s (0,1,2...).
[[category: set theory]]
[[category: set theory]]