In mathematics, the cardinality of a set means the number of its elements. For example, the set A = {2, 4, 6} contains 3 elements, and therefore A has a cardinality of 3. The cardinality of a set A can also be represented as .[1][2]
Two sets have the same (or equal) cardinality if and only if they have the same number of elements, which is the another way of saying that there is a 1-to-1 correspondence between the two sets.[3] The cardinality of the set A is less than or equal to the cardinality of set B if and only if there is an injective function from A to B. The cardinality of the set B is greater than or equal to the cardinality of set A if and only if there is an injective function from A to B.
The cardinality of a set is only one way of giving a number to the size of a set. The concept of measure is yet another way.
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