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Abstract: We introduce a new invariant of a cubic graph – its regular colouring defect – which is defined as the smallest number of edges left uncovered by any collection of three perfect matchings that have no edge in common. This invariant is a modification of colouring defect, an invariant introduced by Steffen in 2025, whose definition does not require the empty intersection condition. In this paper we discuss the relationship of this invariant to the well-known conjectures of Fulkerson (1971) and Fan and Raspaud (1994) and prove that colouring defect and regular colouring defect can be arbitrarily far apart.
Keywords: cubic graph, perfect matching, colouring defect, Fulkerson Conjecture, Fan and Raspaud Conjecture
Published in RUP: 03.03.2026; Views: 394; Downloads: 9
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Abstract: For a finite-dimensional linear subspace ▫{$\mathscr{S}} \subseteq {\mathscr{L}} (V,W)$▫ and a positive integer ▫$k$▫, the ▫$k$▫-reflexivity defect of ▫$\mathscr{S}$▫ is defined by ▫${\mathrm{rd}}_k ({\mathscr{S}}) = \dim({\mathrm{Ref}}_k (\mathscr{S})/\mathscr{S})$▫ where ▫${\mathrm{Ref}}_k$▫ is the ▫$k$▫-reflexive closure of ▫$\mathscr{S}$▫. We study this quantity for two-dimensional spaces of operators and for single generated algebras and their commutants.
Keywords: mathematics, operator theory, reflexivity defect, reflexivity, two-dimensional space of operators, single generated algebra, commutant
Published in RUP: 03.04.2017; Views: 3734; Downloads: 202
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