is serial: for a given , choose .

; Surjective (also called right-total or onto): For all , there exists an such that . For example, the green and blue relations in the diagram are surjective, but the red one is not (as it does not relate any real number to ), nor is the black one (as it does not relate any real number to ).

Combinations of properties

Relations that satisfy certain combinations of the above properties are particularly useful, and thus have received names by their own.

; [[Equivalence

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