===== Singleton =====
==== Set ====
| @#55CCEE: context     | @#55CCEE: $ X $ ... set |
| @#FF9944: definition  | @#FF9944: $ \{X\} \equiv \{X,X\} $ |

==== Discussion ====
=== Reference ===
Wikipedia: [[http://en.wikipedia.org/wiki/Singleton_%28mathematics%29|Singleton]]
==== Parents ====
=== Context* ===
[[Sets]]
=== Requirements ===
[[Unordered pair]]