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In mathematics, a binary relation R over a set X is reflexive if
it relates every element of X to itself.[1][2]

An example of a reflexive relation is the relation "is equal to"
on the set of real numbers, since every real number is equal to itself.

A reflexive relation is said to have the reflexive property or
is said to possess reflexivity. Along with symmetry and transitivity,
reflexivity is one of three properties defining equivalence relations.