===== Idempotent function =====
==== Set ====
| @#55CCEE: context     | @#55CCEE: $X$ ... set |

| @#FFBB00: definiendum | @#FFBB00: $ f\in \mathrm{it}(X) $ |

| @#55EE55: postulate   | @#55EE55: $ f:X\to X $ |
| @#55EE55: postulate   | @#55EE55: $ f\circ f=f $ |

==== Discussion ====
==== Parents ====
=== Subset of ===
[[Unary operation]]