involution

Involution

https://en.wikipedia.org/wiki/Involution_(mathematics)

Involutory function is a function that is its own inverse.

An involution, or an involutory function, is a function ff that is its own inverse, f(f(x))=xf(f(x)) = x

for all xx in the domain of ff

Equivalently, applying ff twice produces the original value.

The term anti-involution refers to involutions based on antihomomorphisms (see Quaternion algebra, groups, semigroups)

f(xy)=f(y)f(x)f(xy) = f(y) f(x) such that

xy=f(f(xy))=f(f(y)f(x))=f(f(x))f(f(y))=xyxy = f(f(xy)) = f( f(y) f(x) ) = f(f(x)) f(f(y)) = xy

Involution

https://en.wikipedia.org/wiki/Involution_(mathematics)

An involution, or an involutory function, is a function f that is its own inverse, f(f(x)) = f(x) (for all x in the domain of f). Equivalently, applying f twice produces the original value.

Any involution is a bijection.

Example of an involuntary function: f(x) = -1 * x

In set theory, involution or double complement law states: (Aᶜ)ᶜ = A

The term *anti-involution refers to involutions based on antihomomorphisms (see Quaternion algebra, groups, semigroups) f(xy) = f(x)f(y) such that xy = f(f(xy)) = f( f(x) f(y) ) = f(f(x)) f(f(y)) = xy

Examples of involution:

  • identity map is a trivial example of an involution

  • multiplication by −1 in arithmetic

  • taking of reciprocals

  • complementation in set theory

  • complex conjugation

  • circle inversion

  • rotation by a half-turn

  • reciprocal ciphers such as the ROT13 transformation

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