The upper chromatic number χ(H) of a hypergraph H is the maximum number of colors in a coloring avoiding a polychromatic edge. The stability number α(H) of a hypergraph H is the cardinality of the largest set of vertices of H which does not contain an edge. A hypergraph is k-uniform if the sizes of all its edges are k. Voloshin conjectured that an r-uniform hypergraph H (r ≥ 3) is co-perfect if and only if it contains neither of two special r-uniform hypergraphs (a so-called monostar and a

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... ete circular r-uniform hypergraph on 2r − 1 vertices) as an induced subhypergraph. We disprove this conjecture for all r. * Institute for Theoretical Computer Science is supported by the Ministry of Education of Czech Republic as project LN00A056.