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Finitely presentable objects in \((Cb\text{-sets})_\mathrm{fs}\). (English) Zbl 07909550

Summary: Pitts generalized nominal sets to finitely supported \(Cb\)-sets by utilizing the monoid \(Cb\) of name substitutions instead of the monoid of finitary permutations over names. Finitely supported \(Cb\)-sets provide a framework for studying essential ideas of models of homotopy type theory at the level of convenient abstract categories.
Here, the interplay of two separate categories of finitely supported actions of a submonoid of \(\operatorname{End}(\mathbb{D})\), for some countably infinite set \(\mathbb{D} \), over sets is first investigated. In particular, we specify the structure of free objects. Then, in the category of finitely supported \(Cb\)-sets, we characterize the finitely presentable objects and provide a generator in this category.

MSC:

08A30 Subalgebras, congruence relations
08C05 Categories of algebras
18A20 Epimorphisms, monomorphisms, special classes of morphisms, null morphisms
18C35 Accessible and locally presentable categories
20M30 Representation of semigroups; actions of semigroups on sets
68Q70 Algebraic theory of languages and automata
Full Text: DOI

References:

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