Canonical form conjecture for binary Δ-matroids under handle slides

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 \floorw2\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.

Sources & referencesView supporting material

Primary source

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

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