Definition:Symmetric Relation

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Definition

Let $\mathcal R \subseteq S \times S$ be a relation in $S$.


Definition 1

$\mathcal R$ is symmetric if and only if:

$\tuple {x, y} \in \mathcal R \implies \tuple {y, x} \in \mathcal R$


Definition 2

$\mathcal R$ is symmetric if and only if it equals its inverse:

$\mathcal R^{-1} = \mathcal R$


Definition 3

$\mathcal R$ is symmetric if and only if it is a subset of its inverse:

$\mathcal R \subseteq \mathcal R^{-1}$


Also see

  • Results about symmetry of relations can be found here.