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Without the axiom of choice, these may not be equivalent. Sets that are neither finite nor Dedekind infinite are called '''amorphous sets'''.
Without the axiom of choice, these may not be equivalent. Sets that are neither finite nor Dedekind infinite are called '''amorphous sets'''.


Within [[ZFC]], the existence of infinite sets is guaranteed by the [[axiom of infinity]], which implies the existence of the natural numbers, which can be proven infinite. Without this axiom, infinite sets can't be proven to exist.
Within [[ZFC]], the existence of infinite sets is guaranteed by the [[axiom of infinity]], which implies the existence of the natural numbers, which can be proven infinite. Without this axiom, infinite sets can't be proven to exist. A model of this theory is provided by the [[hereditarily finite set]]s.


Important kinds of infinite sets include [[countable]] and [[uncountable]] sets.
Important kinds of infinite sets include [[countable]] and [[uncountable]] sets.