Generalised spike-structure conjecture for matroids with the (t1,2t1,t2,2t2)(t_1,2t_1,t_2,2t_2)-property

Let a matroid have the (t1,1,t2,2)(t_1,\ell_1,t_2,\ell_2)-property if every t1t_1-element set is contained in an 1\ell_1-element circuit and every t2t_2-element set is contained in an 2\ell_2-element cocircuit. Let t1t_1 and t2t_2 be positive integers.

Generalised spike-structure conjecture. There exists a function f(t1,t2)f(t_1,t_2) such that if MM is a matroid with the (t1,2t1,t2,2t2)(t_1,2t_1,t_2,2t_2)-property and

E(M)f(t1,t2),|E(M)| \ge f(t_1,t_2),

then E(M)E(M) has a partition into pairs such that the union of any t1t_1 pairs is a circuit, and the union of any t2t_2 pairs is a cocircuit.

This conjecture generalises the structural conclusion for sufficiently large matroids with the (t,2t)(t,2t)-property. It is motivated by examples such as spikes and by results showing that certain sufficiently large matroids with related asymmetric properties form structured classes; the source does not indicate that this conjecture has been resolved.

Sources & referencesView supporting material

Primary source

Nick Brettell, Rutger Campbell, Deborah Chun, Kevin Grace and Geoff Whittle, “On a generalisation of spikes”, arXiv:1804.06959 (2018).

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