The nonexistence of a skein theory for the tangle group functor

Let Tang\mathcal{T}ang be the category of tangles, let ΛGrp\Lambda\mathbf{Grp} be the category of groups, and let Γ ⁣:TangΛGrp\Gamma\colon\mathcal{T}ang\to\Lambda\mathbf{Grp} be the tangle group functor. A skein theory for Γ\Gamma is a finitely generated tensor ideal I\mathcal{I} of Tang\mathcal{T}ang such that Γ\Gamma factors through the canonical projection to Tang/I\mathcal{T}ang/\mathcal{I}; write the induced functor as Γ~ ⁣:Tang/IΛGrp\tilde{\Gamma}\colon\mathcal{T}ang/\mathcal{I}\to\Lambda\mathbf{Grp}. Nonexistence conjecture. There is no skein theory for Γ\Gamma: no finitely generated tensor ideal I\mathcal{I} of Tang\mathcal{T}ang has both the property that Γ\Gamma factors through Tang/I\mathcal{T}ang/\mathcal{I} and the property that Γ~\tilde{\Gamma} is injective. The claim says that the tangle group functor cannot be localized by finitely many tensor-ideal relations while retaining injectivity on the resulting quotient. The supplied text gives no evidence of resolution, so the conjecture is recorded as open.

Sources & referencesView supporting material

Primary source

John Armstrong, “The Extension of Knot Groups to Tangles”, arXiv:math/0509665 (2005).

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