Functoriality of the lasso construction on schemata

A schema is a small category, and for a schema T\mathsf{T}, SetT\mathsf{Set}^{\mathsf{T}} denotes its associated copresheaf category. Let Lasso(SetT)\mathsf{Lasso}(\mathsf{Set}^{\mathsf{T}}) be the category of lassos on that copresheaf category. Lasso functoriality conjecture. There is a contravariant functor

Lasso ⁣:CatCat\mathsf{Lasso} \colon \mathsf{Cat} \to \mathsf{Cat}

which sends every functor F ⁣:STF \colon \mathsf{S} \to \mathsf{T} between schemata to a functor

Lasso(SetT)Lasso(SetS)\mathsf{Lasso}(\mathsf{Set}^{\mathsf{T}}) \to \mathsf{Lasso}(\mathsf{Set}^{\mathsf{S}})

between the corresponding categories of lassos. This would establish a systematic relationship between a schema and the category of lassos on its copresheaf category; the source presents it as a conjecture and does not provide a resolution.

Sources & referencesView supporting material

Primary source

Benjamin Merlin Bumpus, James Fairbanks and Will J. Turner, “Lassos: Pushing Tree Decompositions Forward Along Homomorphisms”, arXiv:2408.15184 (2025).

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