The non-increasing order cover conjecture for torsion classes

Let AA be the algebra under consideration, let g-TF(A)g\text{-}\mathrm{TF}(A) denote the gg-vector fan, let binuc(A)\mathsf{binuc}(A) denote the set of binuclear torsion classes, and let NI\leq_{\mathrm{NI}} be the non-increasing order on torsion classes. For [θ]g-TF(A)[\theta]\in g\text{-}\mathrm{TF}(A), write [θ]\mathsf{\int}[\theta] for the interior of its corresponding face.

Non-increasing cover conjecture. If

[θ]g-TF(A),Ibinuc(A),[θ]NII,[\theta]\in g\text{-}\mathrm{TF}(A),\qquad I\in\mathsf{binuc}(A),\qquad \mathsf{\int}[\theta]\leq_{\mathrm{NI}} I,

then there exists [ρ]g-TF(A)[\rho]\in g\text{-}\mathrm{TF}(A) such that

[θ]< ⁣ ⁣ ⁣ ⁣NI[ρ]NII.[\theta]<\!\!\!\!\cdot_{\mathrm{NI}}[\rho]\leq_{\mathrm{NI}} I.

This would extend the preceding cover theorem from the facial semistability order to the non-increasing order, providing an intermediate gg-vector face between [θ][\theta] and any suitable binuclear torsion class II.

Sources & referencesView supporting material

Primary source

Eric J. Hanson, “A facial order for torsion classes”, arXiv:2305.06031 (2023).

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