“…More specifically, these authors demand: σ(A ∪ B, C) = min{σ(A, C), σ(B, C)} (1) σ(A, B ∩ C) = min{σ(A, B), σ(A, C)}, ∀ A, B, C. 2The above constraints influence the functional expression of σ, and, as a consequence, they implicitly restrict the conditions under which a pair (A, B) satisfies the equality σ(A, B) = 0, as we will prove in this paper. In particular, we will show that Equations 1 and 2 are incompatible with some of the proposals about σ(A, B) = 0 alternatively required by some authors such as Santos et al [11], for example.…”