Stabilized profunctors and stable species of structures
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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.
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