antiadditivity
Antiadditivity is a mathematical property of functions or measures that contrasts with additivity. In an additive system, the value associated with a combined entity equals the sum of the values of its components: f(A ∪ B)=f(A)+f(B) when A and B are disjoint. For an antiadditive function, the opposite inequality holds for all disjoint sets A and B: f(A ∪ B) ≥ f(A)+f(B). This relationship is sometimes called superadditivity. Conversely, when f(A ∪ B) ≤ f(A)+f(B) the function is subadditive, which is distinct from antiadditivity.
In economics antiadditivity is used to model increasing returns to scale, where the benefit of combining inputs
The concept is useful in modeling phenomena where collective performance or risk is greater than the sum