Numerosity (mathematics)

Summary

The numerosity of an infinite set, as initially introduced by the Italian mathematician Vieri Benci and later on extended with the help of Mauro Di Nasso and Marco Forti, is a concept that develops Cantor’s notion of cardinality. While Cantor’s classical cardinality classifies sets based on the existence of a one-to-one correspondence with other sets (defining, for example, $\aleph_0$ for countable sets, $\aleph_1$ and so on for larger infinities), the idea of numerosity aims to provide an alternative viewpoint, linking to the common Euclidean notion that "the whole is greater than the part". All of this naturally leads to the hypernatural numbers.