Definition:Non-Reflexive Relation

Definition

Let $\RR \subseteq S \times S$ be a relation in $S$.

$\RR$ is non-reflexive if and only if it is neither reflexive nor antireflexive.

Also defined as

Some sources define a non-reflexive relation to be a relation which is not reflexive.

Hence, under such a definition, an antireflexive relation would count as being a non-reflexive relation.

Also known as

Some sources use the term irreflexive.

However, as irreflexive is also found in other sources to mean antireflexive, it is better to use the clumsier, but less ambiguous, non-reflexive.

Examples

Arbitrary Non-Reflexive Relation 1

Let $V_1 = \set {y, z}$.

Let $S$ be the relation on $V_1$ defined as:

$S = \set {\tuple {y, y}, \tuple {y, z} }$

Then $S$ is neither:

a reflexive relation, as $\tuple {z, z} \notin S$

nor:

an antireflexive relation, as $\tuple {y, y} \in S$

Thus $S$ is a non-reflexive relation.

Arbitrary Non-Reflexive Relation 2

Let $S = \set {a, b}$.

Let $\RR$ be the relation on $S$ defined as:

$\RR = \set {\paren {a, a} }$

Then $\RR$ is neither:

a reflexive relation, as $\tuple {b, b} \notin \RR$

nor:

an antireflexive relation, as $\tuple {a, a} \in \RR$

Thus $\RR$ is a non-reflexive relation.

Also see

• Results about non-reflexive relations can be found here.