Strongly adjacency-transitive graphs and uniquely shift-transitive graphs

  • Authors:
  • Tomaz Pisanski;Thomas W. Tucker;Boris Zgrablić

  • Affiliations:
  • Univerza v Ljubljani, IMFM/TCS, Jadranska 19, SI-1111 Ljubljana, Slovenia;Colgate University, Department of Mathematics, Hamilton, NY;Pedagoska fakulteta, Univerza v Ljubljani, Kardeljeva ploscad 16, SI-1113 Ljubljana, Slovenia

  • Venue:
  • Discrete Mathematics - Algebraic and topological methods in graph theory
  • Year:
  • 2002

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Abstract

An automorphism σ of a finite simple graph Γ is an adjacency automorphism if for every vertex x ∈ V(Γ), either σx = x or σx is adjacent to x in Γ. An adjacency automorphism fixing no vertices is a shift. A connected graph Γ is strongly adjacency-transitive (respectively, uniquely shift-transitive) if there is, for every pair of adjacent vertices x, y ∈ V(Γ), an adjacency automorphism (respectively, a unique shift) σ ∈ Aut Γ sending x to y. The action graph Γ = ActGrph(G,X,S) of a group G acting on a set X, relative to an inverse-closed nonempty subset S ⊆ G, is defined as follows: the vertex-set of Γ is X, and two different vertices x,y ∈ V(Γ) are adjacent in Γ if and only if y=sx for some s ∈ S. A characterization of strongly adjacency-transitive graphs in terms of action graphs is given. A necessary and sufficient condition for cartesian products of graphs to be uniquely shift-transitive is proposed, and two questions concerning uniquely shift-transitive graphs are raised.