Abstract
Several isomorphism classes of graph coverings of a graph G have been enumerated by many authors (see [3], [8]–[15]). A covering of G is called circulant if its covering graph is circulant. Recently, the authors [4] enumerated the isomorphism classes of circulant double coverings of a certain kind, called typical, and showed that no double covering of a circulant graph of valency 3 is circulant. In this paper, the isomorphism classes of connected circulant double coverings of a circulant graph of valency 4 are enumerated. As a consequence, it is shown that no double covering of a non-circulant graph G of valency 4 can be circulant if G is vertex-transitive or G has a prime power of vertices.
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The first author is supported by NSF of China (No. 60473019) and by NKBRPC (2004CB318000), and the second author is supported by Com2MaC-KOSEF (R11-1999-054) in Korea.
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Feng, R., Kwak, J. Circulant Double Coverings of a Circulant Graph of Valency Four. Graphs and Combinatorics 21, 385–400 (2005). https://doi.org/10.1007/s00373-005-0623-2
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DOI: https://doi.org/10.1007/s00373-005-0623-2