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Medium: Paradox

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Release Message: There is no greatest cardinal number, so the collection of "infinite sizes" is itself infinite. Thus, not only are there infinitely many infinities, but this infinity is larger than any of the infinities it enumerates. Authored by Georg Cantor.

Description: In set theory, Cantor's paradox is derivable from the theorem that there is no greatest cardinal number, so that the collection of "infinite sizes" is itself infinite. The difficulty is handled in axiomatic set theory by declaring that this collection is not a set but a proper class; in von Neumann_Bernays_G_del set theory it follows from this and the axiom of limitation of size that this proper class must be in bijection with the class of all sets. Thus, not only are there infinitely many infinities, but this infinity is larger than any of the infinities it enumerates. This paradox is named for Georg Cantor, who is often credited with first identifying it in 1899 (or between 1895 and 1897). Like a number of "paradoxes" it is not actually contradictory but merely indicative of a mistaken intuition, in this case about the nature of infinity and the notion of a set. Put another way, it is paradoxical within the confines of na¥ve set theory and therefore demonstrates that a careless axiomatization of this theory is inconsistent. (Naive set theory)