Climb into Cantor’s Attic, where you will find infinities large and small. We aim to provide a comprehensive resource of information about all notions of mathematical infinity.

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Zero, or $0$, is the smallest ordinal (and cardinal) number. It is usually represented by the empty set, $\varnothing$ (or $\{\}$).

Given an ordinal (or cardinal) $x$:

Most set theorists classify zero as the only ordinal which is neither a limit ordinal nor the successor of any ordinal.

Some set theorists (e.g. Thomas Jech) instead classify zero as a limit ordinal, because like other limit ordinals, it is the limit of all ordinals less than it (of which there are none).