Título: Solidarity to achieve stability
Abstract: Agents belong to coalitions. Each coalition shares its endowment among its agents by applying a sharing rule. The sharing rule induces a coalition formation problem by assuming that agents rank coalitions according to the allocation they obtain in the corresponding sharing problem. We characterize the sharing rules that induce a class of coalition formation problems that induce stability as those satisfying a natural axiom formalizing the principle of solidarity. Thus, solidarity becomes a sufficient condition to achieve stability.