We study two kinds of containers for data types with symmetries in homotopy type theory, and clarify their relationship by introducing the intermediate notion of action containers. Quotient containers are set-valued containers with groups of permissible permutations of positions, interpreted as (possibly non-finitary) analytic functors on the category of sets. Symmetric containers encode symmetries in a groupoid of shapes, and are interpreted accordingly as polynomial functors on the 2-category of groupoids. Action containers are endowed with groups that act on their positions, with morphisms preserving the actions. We show that, as a category, action containers are equivalent to the free coproduct completion of a category of group actions. We derive that they model non-inductive single-variable strictly positive types in the sense of Abbott et al.: The category of action containers is closed under arbitrary (co)products and exponentiation with constants. We equip this category with the structure of a locally groupoidal 2-category, and prove that it locally embeds into the 2-category of symmetric containers. This follows from the embedding of a 2-category of groups into the 2-category of groupoids, extending the delooping construction.
@InProceedings{joram_et_al:LIPIcs.TYPES.2024.6, author = {Joram, Philipp and Veltri, Niccol\`{o}}, title = {{Data Types with Symmetries via Action Containers}}, booktitle = {30th International Conference on Types for Proofs and Programs (TYPES 2024)}, pages = {6:1--6:21}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-376-8}, ISSN = {1868-8969}, year = {2025}, volume = {336}, editor = {M{\o}gelberg, Rasmus Ejlers and van den Berg, Benno}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TYPES.2024.6}, URN = {urn:nbn:de:0030-drops-233681}, doi = {10.4230/LIPIcs.TYPES.2024.6}, annote = {Keywords: Containers, Homotopy Type Theory, Agda, 2-categories} }
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