1. Groups with elements of order 8 do not have the DCI propertyTed Dobson, Joy Morris, Pablo Spiga, 2025, original scientific article Abstract: Let k be odd, and n an odd multiple of 3. Although this can also be deduced from known results, we provide a new proof that Ck ⋊ C₈ and (Cn × C₃) ⋊ C₈ do not have the Directed Cayley Isomorphism (DCI) property. When k is prime, Ck ⋊ C₈ had previously been proved to have the Cayley Isomorphism (CI) property. To the best of our knowledge, the groups Cp ⋊ C₈ (where p is an odd prime) are only the second known infinite family of groups that have the CI property but do not have the DCI property. This also provides a new proof of the result (which follows from known results but was not explicitly published) that no group with an element of order 8 has the DCI property.
One piece of our proof is a new result that may prove to be of independent interest: we show that if a permutation group has a regular subgroup of index 2 then it must be 2-closed.
Keywords: CI property, DCI property, Cayley graphs, Cayley digraphs, 2-closed groups, 2-closure
Published in RUP: 03.11.2025; Views: 211; Downloads: 1
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3. A census of 4-valent half-arc-transitive graphs and arc-transitive digraphs of valence two : dedicated to Dragan Marušič on the occasion of his 60th birthdayPrimož Potočnik, Pablo Spiga, Gabriel Verret, 2015, original scientific article Abstract: A complete list of all connected arc-transitive asymmetric digraphs of in-valence and out-valence 2 on up to 1000 vertices is presented. As a byproduct, a complete list of all connected 4-valent graphs admitting a half-arc-transitive group of automorphisms on up to 1000 vertices is obtained. Several graph-theoretical properties of the elements of our census are calculated and discussed.
Keywords: graphs, digraphs, edge-transitive, vertex-transitive, arc-transitive, half arc-transitive
Published in RUP: 31.12.2021; Views: 2246; Downloads: 19
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8. Set graphs. II. Complexity of set graph recognition and similar problemsMartin Milanič, Romeo Rizzi, Alexandru I. Tomescu, 2014, original scientific article Keywords: acyclic orientation, extensionality, set graphs, NP-complete problem, #P-complete problem, hyper-extensional digraphs, separating code, open-out-separating code
Published in RUP: 03.04.2017; Views: 3600; Downloads: 136
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9. A note on a conjecture on consistent cyclesŠtefko Miklavič, 2013, original scientific article Abstract: Let ▫$\Gamma$▫ denote a finite digraph and let ▫$G$▫ be a subgroup of its automorphism group. A directed cycle ▫$\vec{C}$▫ of▫ $\Gamma$▫ is called ▫$G$▫-consistent whenever there is an element of ▫$G$▫ whose restriction to▫ $\vec{C}$▫ is the 1-step rotation of ▫$\vec{C}$▫. In this short note we provea conjecture on ▫$G$▫-consistent directed cycles stated by Steve Wilson.
Keywords: graph theory, digraphs, consistent directed cycles
Published in RUP: 15.10.2013; Views: 4260; Downloads: 133
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