# What is Inverse Relation – Definition & Example

Here you will learn what is inverse relation, identity relation and posets in relation with example.

Let’s begin –

## Definition of Inverse Relation

If relation R is defined from A to B, then inverse relation would be defined form B to A, i.e.

R : A $$\rightarrow$$ B $$\implies$$ aRb where a $$\in$$ A, b $$\in$$ B

$$R^{-1}$$ : B $$\rightarrow$$ A $$\implies$$ bRa where a $$\in$$ A, b $$\in$$ B

Domain of R = Range of $$R^{-1}$$

and  Range of R = Domain of $$R^{-1}$$

$$\therefore$$   $$R^{-1}$$ = {(b, a) | (a, b) $$\in$$ R}

A relation R is defined on the set of 1st ten natural numbers.

e.g.   N is a set of first 10 natural numbers.

aRb $$\implies$$ a + 2b = 10

R = {(2, 4), (4, 3), (6, 2), (8, 1)}

$$R^{-1}$$ = {(4, 2), (3, 4), (2, 6), (1, 8)}

## Identity Relation

A relation defined on a set A is said to be an identity relation if each and every element of A is related to itself & only to itself.

e.g.  A relation defined on the set of natural numbers is

aRb $$\implies$$ a = b where a & b $$\in$$ N

R = {(1, 1), (2, 2), (3, 3), ……}

R is an identity relation

## Posets

A relation R on a set P is called an partial relation order if it is reflexive, antisymmetric and transitive. That means that for all x, y and z in P we have:

• x R x;
• if x R y and y R x, then x = y;
• if x R y and y R z, then x R z.

The pair (P, R) is called a partially ordered set, or for short, a poset.

Two elements x and y in a poset (P, R) are called comparable if x R y or y R x.

If any two elements x,y $$\in$$ P are comparable, so we have x R y or y R x, then the relation is called a linear order.