°Of a relationR on a setS, such that xRyif and only ifyRx for all membersx and y of S (that is, if the relation holds between any element and a second, it also holds between the second and the first).
°Of a relationR on a setS, such that xRyif and only ifyRx for all membersx and y of S (that is, if the relation holds between any element and a second, it also holds between the second and the first).