Two-player incentive compatible mechanisms are affine maximizers

In mechanism design, for a given type space, there may be incentive compatible mechanisms which are not affine maximizers. We prove that for two-player games on a discrete type space, any given mechanism can be turned into an affine maximizer through a nontrivial perturbation of the type space. Furthermore, our theorem is the strongest possible in this setup. Our proof relies on new results on the tropical determinant.