Let us define the heterogeneity H(X) of a set of measures X as, given two system outputs s and s such that g = s = s = g (g is the reference text), the probability that there exist two measures that contradict each other.
that is: given a set X of measures, the property states that there exists a strict growing function F such that: In other words, the more the similarity measures tend to contradict each other, the more a unanimous improvement over all similarity measures is reliable.