AntiSymmetry

In mathematics, a homogeneous relation R on set X is antisymmetric if there is no pair of distinct elements of X each of which is related by R to the other. More formally, R is antisymmetric precisely if for all a and b in X.

If R(a,b) holds then R(b,a) must not hold

or equivalently: if R(a,b) == R(b,a) then a==b