Editing Bijection (section)

==Cardinality==
If ''X'' and ''Y'' are [[finite set]]s, then there exists a bijection between the two sets ''X'' and ''Y'' [[if and only if]] ''X'' and ''Y'' have the same number of elements. Indeed, in [[axiomatic set theory]], this is taken as the definition of "same number of elements" ([[equinumerosity]]), and generalising this definition to [[infinite set]]s leads to the concept of [[cardinal number]], a way to distinguish the various sizes of infinite sets.