A Fibrational Framework For Multi-Conclusion Logics
Oualid Merzouga
The fibrational framework of Licata, Shulman, and Riley gives a uniform account of substructural and modal logics for single-conclusion judgments. This thesis extends it to a multiple-output setting in which cartesian resources may be used freely, while linear resources occur exactly once on either side of the turnstile. Judgments are indexed by descriptors: directed acyclic graphs generalizing the tree-shaped expressions of the original framework. Descriptor $2$-cells encode structural transformations, and explicit gates provide weakening, contraction, coweakening, and cocontraction at linear modes. We define a sequent calculus generated by two connectives, $F$ and $U$. We prove identity, invertibility, and cut admissibility. The mode and type theories present linear-non-linear $2$-polycategories, and the projection is a local discrete fibration and a fibration, with opcartesian lifts for one-output base morphisms. Two adequacy results validate the framework: its cartesian fragment recovers the Licata--Shulman--Riley calculus, and its purely linear fragment presents classical multiplicative linear logic. Finally, we relate indexed and fibrational semantics. After developing representability correspondences for multicategories and polycategories, we establish an equivalence between multi-indexed categories over a fixed representable base and multicategorical opfibrations over it, together with its biclosed bifibrational version. We also give a one-way construction from planar poly-indexed data to a planar polycategory.
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