The simultaneous breadth-preserving minor conjecture for tangle truncations

Let MM be a matroid with a tangle T\mathcal{T} of order k4k\geq 4. For each i{4,5,,k}i\in\{4,5,\ldots,k\}, let Ti(T)T_i(\mathcal{T}) be the truncation of T\mathcal{T} to order ii. The simultaneous breadth-preserving minor conjecture. There is a (0,1,4)(0,1,4)-connected minor NN of MM such that, for all i{4,5,,k}i\in\{4,5,\ldots,k\}, the tangle Ti(T)T_i(\mathcal{T}) generates a tangle Ti(T)T'_i(\mathcal{T}) in NN, and

breadthM(Ti(T))=breadthN(Ti(T)).\operatorname{breadth}_M(T_i(\mathcal{T}))=\operatorname{breadth}_N(T'_i(\mathcal{T})).

This asks for one weakly 44-connected minor that simultaneously preserves the breadths of all truncations of a tangle; the paper leaves this simultaneous reduction open.

Sources & referencesView supporting material

Primary source

Nick Brettell, Susan Jowett, James Oxley, Charles Semple and Geoff Whittle, “What is a 4-connected matroid?”, arXiv:2310.08832 (2025).

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