15 research outputs found

    An update on the Hirsch conjecture

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    The Hirsch conjecture was posed in 1957 in a letter from Warren M. Hirsch to George Dantzig. It states that the graph of a d-dimensional polytope with n facets cannot have diameter greater than n - d. Despite being one of the most fundamental, basic and old problems in polytope theory, what we know is quite scarce. Most notably, no polynomial upper bound is known for the diameters that are conjectured to be linear. In contrast, very few polytopes are known where the bound ndn-d is attained. This paper collects known results and remarks both on the positive and on the negative side of the conjecture. Some proofs are included, but only those that we hope are accessible to a general mathematical audience without introducing too many technicalities.Comment: 28 pages, 6 figures. Many proofs have been taken out from version 2 and put into the appendix arXiv:0912.423

    Hirschmanniella nom. nov. for Hirschmannia

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    Preferência do bicudo-das-palmeiras por dendezeiro, caiaué e por seu híbrido interespecífico

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    O objetivo deste trabalho foi determinar, em campo, a preferência do bicudo-das-palmeiras (Rhynchophorus palmarum) por estipes de dendezeiro (Elaeis guineensis), caiaué (Elaeis oleifera) e pelo híbrido entre caiaué e dendezeiro. O experimento foi conduzido no banco de germoplasma de dendê da Comissão Executiva de Planejamento da Lavoura Cacaueira. Entre os três genótipos testados, o caiaué é significativamente menos preferido por Rhynchophorus palmarum, seguido do híbrido interespecífico e do dendezeiro
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