Permutahedra and generalized associahedra. (Q610689)

Suppose that \((W,S)\) is a finite Coxeter system and \(c\in W\) is a Coxeter element (a product of the simple reflections in some order). \textit{N. Reading} [Adv. Math. 205, No. 2, 313-353 (2006; Zbl 1106.20033)] has associated to this data the corresponding \(c\)-Cambrian fan \(\mathcal F_c\) and conjectured that every such fan is the normal fan of a polytope. The main result of this article is a proof of this conjecture, via the construction of a \(c\)-generalized associahedron. Note that Cambrian fans are known to be linearly isomorphic to \(\mathbf g\)-vector fans of finite type cluster algebras with respect to an acyclic initial seed. This was proved by \textit{N. Reading} and \textit{D. E. Speyer} [in J. Eur. Math. Soc. 11, No. 2, 407-447 (2009; Zbl 1213.20038)] modulo a conjecture of \textit{S. Fomin} and \textit{A. Zelevinsky} [Compos. Math. 143, No. 1, 112-164 (2007; Zbl 1127.16023)] which was later proved by \textit{S.-W. Yang} and \textit{A. Zelevinsky} [Transform. Groups 13, No. 3-4, 855-895 (2008; Zbl 1177.16010)].