Relation defined in a set E so that, for every ordered pair of elements (x, y) of \(E\times E\), if x is in relation with y, then y is in relation with x.
- The arrow diagram of a symmetric relation in a set E includes a return arrow every time that there is an arrow going between two elements.
- A relation defined in a set E so that, for every ordered pair (x, y) of E \(\times\) E, with x ≠ y, (y, x) is not an ordered pair of the relation, is called an antisymmetric relation.
- A relation defined in a set E that is neither symmetric nor antisymmetric is a non-symmetric relation.
- A relation defined in a set E so that, for all pairs of elements {x, y}, either one of the ordered pairs (x, y) or (y, x) belong to the relation, but never both at the same time, is an asymmetric relation.
Examples
- In a set of lines of a plane, the relation “…is perpendicular to…” is a symmetric relation.
- In a set of numbers, the relation “…divides…” is an antisymmetric relation.
- In a set of numbers, the relation “…is less than…” is an asymmetric relation.