# Inverse Relation

An Inverse Relation is a Binary Relation between Binary Relations where the Variable order is switched.

**AKA:**Inverse Function.**Context:**- A Inverse(Reflexive Relation
*R'*() ) ⇒ Reflexive Relation*R"*().

- A Inverse(Reflexive Relation
**Example(s):****Counter-Example(s):****See:**Directed Relation, Transpose, Binary Relation, Unary Operation, Involution (Mathematics).

## References

### 2015

- (Wikipedia, 2015) ⇒ http://en.wikipedia.org/wiki/inverse_function Retrieved:2015-12-30.
- In mathematics, an
**inverse function**is a function that "reverses" another function. That is, if is a function mapping to, then the inverse function of maps back to .

- In mathematics, an

- (Wikipedia, 2015) ⇒ http://en.wikipedia.org/wiki/inverse_relation Retrieved:2015-12-30.
- In mathematics, the
**inverse relation**of a binary relation is the relation that occurs when the order of the elements is switched in the relation. For example, the inverse of the relation 'child of' is the relation 'parent of'. In formal terms, if [math] X \text{ and } Y [/math] are sets and [math] L \subseteq X \times Y [/math] is a relation from*X*to Y*then [math] L^{-1} [/math] is the relation defined so that [math] y\,L^{-1}\,x [/math] if and only if [math] x\,L\,y [/math] . In set-builder notation, [math] L^{-1} = \{(y, x) \in Y \times X \mid (x, y) \in L \} [/math] .**The notation comes by analogy with that for an inverse function. Although many functions do not have an inverse; every relation does have a unique inverse. Despite the notation and terminology, the inverse relation is*not*an inverse in the sense of group inverse; the unary operation that maps a relation to the inverse relation is however an involution, so it induces the structure of a semigroup with involution on the binary relations on a set, or more generally induces a dagger category on the category of relations as detailed below. As a unary operation, taking the inverse (sometimes called**inversion) commutes however with the order-related operations of relation algebra, i.e. it commutes with union, intersection, complement etc.**The inverse relation is also called the*L**converse relation**or**transpose relation**— the latter in view of its similarity with the transpose of a matrix.^{[1]}It has also been called the opposite or**dual**of the original relation. Other notations for the inverse relation includeC^{}*,*LT^{}*,*LL^{~}or [math] \breve{L} [/math] or*° or*L^{∨}.

- In mathematics, the

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