Hard Enumeration Problems in Geometry and Combinatorics
Nathan Linial · SIAM Journal on Algebraic and Discrete Methods · 1986
A number of natural enumeration problems in geometry and combinatorics are shown to be complete in the class # P introduced by Valiant. Among others this is established for the numeration of vertices and of facets of a polytope, acyclic orientations of a graph and satisfying assignments of implicative boolean formulas.