Excluded-minor conjecture for 3-regular matroids

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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, P8−P_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.

References

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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