Symmetric relation
A symmetric relation is a type of binary relation. Formally, a binary relation R {\displaystyle R} on a set X {\displaystyle X} is symmetric if: for all a {\displaystyle a} and b {\displaystyle b} in X {\displaystyle X} , a R b {\displaystyle aRb} if and only if b R a {\displaystyle bRa} , where the notation a R b {\displaystyle aRb} means that the ordered pair ( a , b ) {\displaystyle (a,b)} is in the relation R {\displaystyle R} .