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Abstract: An abstract n-polytope P is a partially-ordered set which captures important properties of a geometric polytope, for any dimension n. For even n ≥ 2, the incidences between elements in the middle two layers of the Hasse diagram of P give rise to the medial layer graph of P, denoted by G = G(P). If n = 4, and P is both highly symmetric and self-dual of type {p, q, p}, then a Cayley graph C covering G can be constructed on a group of polarities of P. In this paper we address some open questions about the relationship between G and C that were raised in a 2008 paper by Monson and Weiss, and describe some interesting examples of these graphs. In particular, we give the first known examples of improperly self-dual chiral polytopes of type {3, q, 3}, which are also among the very few known examples of highly symmetric self-dual finite polytopes that do not admit a polarity. Also we show that if p = 3 then C cannot have a higher degree of s-arc-transitivity than G, and we present a family of regular 4-polytopes of type {6, q, 6} for which the vertex-stabilisers in the automorphism group of C are larger than those for G.
Keywords: abstract polytope, regular polytope, chiral polytope, medial graph
Published in RUP: 16.09.2025; Views: 908; Downloads: 22
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Abstract: A cycle decomposition of a graph ▫$\Gamma$▫ is a set ▫$\mathcal{C}$▫ of cycles of ▫$\Gamma$▫ such that every edge of ▫$\Gamma$▫ belongs to exactly one cycle in ▫$\mathcal{C}$▫. Such a decomposition is called arc-transitive if the group of automorphisms of ▫$\Gamma$▫ that preserve setwise acts transitively on the arcs of ▫$\Gamma$▫. In this paper, we study arc-transitive cycle decompositions of tetravalent graphs. In particular, we are interested in determining and enumerating arc-transitive cycle decompositions admitted by a given arc-transitive tetravalent graph. Among other results we show that a connected tetravalent arc-transitive graph is either 2-arc-transitive, or is isomorphic to the medial graph of a reflexible map, or admits exactly one cycle structure.
Keywords: mathematics, graph theory, cycle decomposition, automorphism group, consistent cycle, medial maps
Published in RUP: 15.10.2013; Views: 8860; Downloads: 92
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