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1.
Cycle separating cuts in possible counterexamples to the cycle double cover and the Berge-Fulkerson conjectures
Edita Máčajová, Giuseppe Mazzuoccolo, Gloria Tabarelli, 2026, original scientific article

Abstract: It is known that smallest counterexamples to the Cycle Double Cover Conjecture and Berge-Fulkerson Conjecture (if they exist) are cyclically 4- and 5-edge-connected, respectively. We further analyse small cycle separating cuts in possible counterexamples. We prove that if a smallest counterexample G to the CDC Conjecture contains a cycle separating 4-cut S, then the behaviour of the admissible CDC coverings along the dangling edges of the two 4-poles induced by S is uniquely determined among more than 2 a priori possibilities. Similarly, for the Berge-Fulkerson Conjecture, we prove that among more than 2 a priori possibilities, there are only 13 pairs of admissible sets that could occur along the dangling edges of a 5-cut in a smallest counterexample.
Keywords: snark, cyclic connectivity, cycle double cover, Berge-Fulkerson conjecture
Published in RUP: 03.03.2026; Views: 485; Downloads: 16
.pdf Full text (412,02 KB)

2.
Regular colouring defect of a cubic graph and the conjectures of Fan-Raspaud and Fulkerson
Ján Karabáš, Edita Máčajová, Roman Nedela, Martin Škoviera, 2026, original scientific article

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: 420; Downloads: 12
.pdf Full text (313,05 KB)

3.
6-decomposition of snarks
Ján Karabáš, Edita Máčajová, Roman Nedela, 2013, original scientific article

Keywords: dekompozicije, graf, barvanje, decompositions, graphs, coloring
Published in RUP: 15.10.2015; Views: 4850; Downloads: 115
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