ISSN 1234-3099 (print version)

ISSN 2083-5892 (electronic version)

Discussiones Mathematicae Graph Theory

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Discussiones Mathematicae Graph Theory


Discussiones Mathematicae Graph Theory 21(1) (2001) 13-30
DOI: 10.7151/dmgt.1130


Ivan Havel

Mathematical Institute, Academy of Sciences of the Czech Republic
Zitná 25, 115 67 Prague 1, Czech Republic

Bohdan Zelinka

Technical University
Voronezská 13, 461 17 Liberec, Czech Republic



We deal with the graph operator [`(Pow2)] defined to be the complement of the square of a graph: [`(Pow2)](G) = [`(Pow2(G))]. Motivated by one of many open problems formulated in [6] we look for graphs that are 2-periodic with respect to this operator. We describe a class G of bipartite graphs possessing the above mentioned property and prove that for any m,n ≥ 6, the complete bipartite graph Km,n can be decomposed in two edge-disjoint factors from G. We further show that all the incidence graphs of Desarguesian finite projective geometries belong to G and find infinitely many graphs also belonging to G among generalized hypercubes.

Keywords: graph operator, power and complement of a graph, Desarguesian finite projective geometry, decomposition of a complete bipartite graph, generalized hypercube.

2000 Mathematics Subject Classification: 05C38, 05C75.


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Received 27 December 1999
Revised 19 October 2000