ABSTRACT
A two-place relation R for which, with regard to any objects x and y, it is true: R(x, y)→R(y, x). This is the case, for example, for the relation of ‘being married’: if x is married to y, then y is also married to x. If both pairs in the relation cannot be reversed in any case, then the relation is not symmetrical: for example, x is the sister of y cannot be reversed to y is the sister of x, if y=[+male]. A relation R is asymmetric, if there are not two objects x and y for which both R(x, y) as well as R(y, x) is the case; for example, this is the case in the relation ‘is the daughter of.’
