Empty set

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2020 Mathematics Subject Classification: Primary: 03E [MSN][ZBL]

The set which contains no elements. Notation: $\emptyset$, $\{\}$, $\Lambda$. In other words, $\{x:x\neq x\}$. Moreover, any assertion that is always false could be used in this definition instead of $x\neq x$. The statement $x \in \emptyset$ is always false. The empty set is a subset of any set.


[a1] P. R. Halmos, Naive Set Theory, Springer (1960) ISBN 0-387-90092-6
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This article was adapted from an original article by M.I. Voitsekhovskii (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article