Excluded-minor conjecture for 3-regular matroids

Let MM be a matroid. A matroid is 33-regular if it has a representation over Q(α1,α2,α3)\mathbb{Q}(\alpha_1,\alpha_2,\alpha_3) in which every non-zero subdeterminant is an integer power of a difference of distinct members of {0,1,α1,α2,α3}\{0,1,\alpha_1,\alpha_2,\alpha_3\}. Let Δ()(U2,7)\Delta^{(*)}(U_{2,7}) denote the family of six matroids obtained from U2,7U_{2,7} by Δ\Delta-YY exchange and dualising. Excluded-minor conjecture for 33-regular matroids. A matroid MM is 33-regular if and only if it has no minor isomorphic to one of the following 3333 matroids:

F7,F7,F7=,H7,M(K4)+e,W3+e,Λ3,Q6+e,P6+e,U3,7,F_7, F_7^-, F_7^=, H_7, M(K_4)+e, \mathcal{W}^3+e, \Lambda_3, Q_6+e, P_6+e, U_{3,7},

and their duals; a matroid in Δ()(U2,7)\Delta^{(*)}(U_{2,7}); and AG(2,3)\e\mathit{AG}(2,3)\backslash e, (AG(2,3)\e)(\mathit{AG}(2,3)\backslash e)^*, (AG(2,3)\e)ΔY(\mathit{AG}(2,3)\backslash e)^{\Delta Y}, P8P_8, P8P_8^-, P8=P_8^=, and TQ8\mathit{TQ}_8. The conjecture would provide the excluded-minor characterisation for 33-regular matroids, complementing the proved characterisation for 22-regular matroids; the listed excluded minors are known up to size 1313, while completeness of the list remains open.

Sources & referencesView supporting material

Primary source

Nick Brettell, James Oxley, Charles Semple and Geoff Whittle, “The excluded minors for 2- and 3-regular matroids”, arXiv:2206.15188 (2023).

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