# Singleton

From Encyclopedia of Mathematics

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

A set which contains exactly one element. Notation: $\{ x \}$. One has $y \in \{ x \} \Leftrightarrow y = x$.

#### References

[1] | P. R. Halmos, Naive Set Theory, Springer (1960) ISBN 0-387-90092-6 |

**How to Cite This Entry:**

Singleton.

*Encyclopedia of Mathematics.*URL: http://encyclopediaofmath.org/index.php?title=Singleton&oldid=53851