Equinumerosity
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Two sets A and B are equinumerous if they have the same cardinality, i.e., if there exists a bijection f : A → B. This is usually denoted
- <math>A \approx B<math>.
The study of cardinality is often called equinumerosity. Sometimes the terms equipotent or equipollent are used.
In Set, the category of all sets with functions as morphisms, an isomorphism between two sets is precisely a bijection, and two sets are equinumerous precisely if they are isomorphic in this category.