(i) | $f$ is an D976: Invertible map |

(ii) | $f^{-1}$ is an D216: Inverse map of $f$ |

**involution**if and only if \begin{equation} f = f^{-1} \end{equation}

▾ Set of symbols

▾ Alphabet

▾ Deduction system

▾ Theory

▾ Zermelo-Fraenkel set theory

▾ Set

▾ Binary cartesian set product

▾ Binary relation

▾ Inverse binary relation

▾ Inverse map

▾ Alphabet

▾ Deduction system

▾ Theory

▾ Zermelo-Fraenkel set theory

▾ Set

▾ Binary cartesian set product

▾ Binary relation

▾ Inverse binary relation

▾ Inverse map

Formulation 2

Let $f : X \to X$ be a D18: Map such that

Then $f$ is an **involution** if and only if
\begin{equation}
f = f^{-1}
\end{equation}

(i) | $f$ is an D976: Invertible map |

(ii) | $f^{-1}$ is an D216: Inverse map of $f$ |

Results