Unique square property and fundamental factorizations of graph bundles

  • Authors:

  • Blaz Zmazek;Janez Zerovnik

  • Affiliations:

  • Department of mathematics, University of Maribor, PEF, Koroska cesta 160, 2000 Maribor, Slovenia and Institute of Mathematics, Physics and Mechanics, Department of Theoretical Computer Science, Ja ...;Faculty of Mechanical Engineering, University of Maribor, FS, Smetanova 17, 2000 Maribor, Slovenia and Institute of Mathematics, Physics and Mechanics, Department of Theoretical Computer Science, ...

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

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Abstract

Graph bundles generalize the notion of covering graphs and graph products. In Imrich et al. (Discrete Math. 167/168 (1998) 393) authors constructed an algorithm that finds a presentation as a nontrivial cartesian graph bundle for all graphs that are cartesian graph bundles over triangle-free simple base using the relation δ* having the square property. An equivalence relation R on the edge set of a graph has the (unique) square property if and only if any pair of adjacent edges which belong to distinct R-equivalence classes span exactly one induced 4-cycle (with opposite edges in the same R-equivalence class). In this paper we define the unique square property and show that any weakly 2-convex equivalence relation possessing the unique square property determines the fundamental factorization of a graph as a nontrivial cartesian graph bundle over an arbitrary base graph, whenever it separates degenerate and nondegenerate edges of the factorization.