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We introduce a new bicategorical model of linear logic based on profunctors between groupoids. This model is a new variation of the usual bicategory of profunctors, obtained by endowing groupoids with additional structure to constrain the profunctors. One goal of this new model is to provide a formal bridge between the model of finitary polynomial functors, also known as normal functors, and the combinatorial theory of generalized species of structures. Our approach consists in viewing finitary polynomial functors as analytic functors generated by free generalized species. The main conceptual novelty is the notion of kit, designed to control the extent to which species are free. We study kits from both combinatorial and logical perspectives. Profunctors that respect the kit structure are called stabilized, and the bicategory of stabilized profunctors gives rise to stable species of structures, a cartesian closed bicategory that embeds finitary polynomial functors. Stabilized profunctors and stable species can be given an extensional presentation as certain functors between subcategories of presheaves determined by the kit. This gives a strict 2-categorical presentation of the same model., Comment: 50 pages, long version of 10.4230/LIPIcs.FSCD.2022.31

This paper studies presentations of the Sierpinski gasket as a final coalgebra for functors on several categories of metric spaces with additional designated points. The three categories which we study differ on their morphisms: one uses short (non-expanding) maps, a second uses Lipschitz maps, and a third uses continuous maps. The functor in all cases is very similar to what we find in the standard presentation of the gasket as an attractor. We prove that the Sierpinski gasket itself is the final coalgebra of a naturally-occurring functor in the continuous setting. In the short setting, the final coalgebra exists but it is better described as the completion of the initial algebra, and this is not isomorphic to the Sierpinski gasket. In the Lipschitz setting, the final coalgebra does not exist. We determine the initial algebras in all three settings as well., 21 pages