Canonical form conjecture for binary Δ-matroids under handle slides

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Let DD be a binary Δ\Delta-matroid. A handle slide is the operation that replaces DD by DabD_{ab} for distinct elements a,ba,b of its ground set, as defined by the feasible-set transformation in the source. Let Di,j,k,lD_{i,j,k,l} be the direct sum of Di,j,kD_{i,j,k} with ll copies of ({e},{{e}})(\{e\},\{\{e\}\}), where Di,j,kD_{i,j,k} is the direct sum of ii copies of ({e},{∅})(\{e\},\{\emptyset\}), jj copies of ({e,f},{∅,{e,f}})(\{e,f\},\{\emptyset,\{e,f\}\}), and kk copies of ({e},{∅,{e}})(\{e\},\{\emptyset,\{e\}\}). For a binary Δ\Delta-matroid, call it even when all feasible sets have the same parity of cardinality, and write ww for the difference between the sizes of a largest and a smallest feasible set.

Canonical form conjecture. For each binary Δ\Delta-matroid DD, there is a sequence of handle slides taking DD to some Di,j,k,lD_{i,j,k,l} where ii is the size of the ground set minus the size of a largest feasible set, ll is the size of a smallest feasible set, and 2j+k2j+k is the difference in the sizes of a largest and a smallest feasible set. Moreover, k=0k=0 if and only if DD is even, and if DD is odd then every value of jj from 00 to \floor∗w2\floor*{\frac{w}{2}} can be attained.

This conjecture proposes a canonical classification of binary Δ\Delta-matroids under handle slides, with the parameters constrained by the extremal feasible-set sizes and parity. The supplied text does not state whether the conjecture has been proved or disproved.

References

Primary source

Rémi Cocou Avohou, Brigitte Servatius and Herman Servatius, “Canonical binary Δ-matroids”, arXiv:2203.04365 (2022).

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