"[...] We saw that unacceptability and ties are a major source of intractability when computing Pareto optimal outcomes. In some cases, checking whether a given partition is Pareto optimal can be significantly harder than finding one.[...]" (Aziz et al., 2013)
So now I have a small question. Is it possible to conclude that all coalition games have a Pareto optimal solution, even though it is maybe extremely hard to find that solution, or is it possible that for some coalition games, a Pareto optimal solution may not exist?
Aziz, Haris, Felix Brandt, and Paul Harrenstein. "Pareto optimality in coalition formation." Games and Economic Behavior 82 (2013): 562-581.