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Tuesday, September 8, 2015

**Abstract:** Group spectra are the group objects in Kan's category of semisimplicial spectra. They provide an algebraic, combinatorial model for the stable homotopy category. After introducing Kan's category of spectra, we will construct the analogues of Kan's loop group functor, of its right adjoint Wbar and corresponding classifying bundles such that the category of semisimplicial spectra becomes a twisted homotopical category in the sense of Farjoun and Hess. This will enable us to formulate and study an up-to-homotopy notion of normal subgroup spectra.