Abstract
The following conjecture may have never been explicitly stated, but seems to have been floating around: if the vertex set of a graph with maximal degree Δ is partitioned into sets V i of size 2Δ, then there exists a coloring of the graph by 2Δ colors, where each color class meets each V i at precisely one vertex. We shall name it the strong 2Δ-colorability conjecture. We prove a fractional version of this conjecture. For this purpose, we prove a weighted generalization of a theorem of Haxell, on independent systems of representatives (ISR’s). En route, we give a survey of some recent developments in the theory of ISR’s.
Similar content being viewed by others
References
R. Aharoni: Ryser’s conjecture for 3-partite 3-graphs, Combinatorica 21(1) (2001), 1–4.
R. Aharoni, E. Berger and R. Ziv: A tree version of König’s theorem, Combinatorica 22(3) (2002), 335–343.
R. Aharoni, M. Chudnovsky and A. Kotlov: Triangulated spheres and colored cliques, Disc. Comput. Geometry 28 (2002), 223–229.
R. Aharoni and M. Chudnovsky: Special triangulations of the simplex and systems of disjoint representatives, unpublished.
R. Aharoni and P. Haxell: Hall’s theorem for hypergraphs, J. of Graph Theory 35 (2000), 83–88.
A. Björner: Topological methods, in: Handbook of Combinatorics (R. Graham, M. Grötschel and L. Lovász editors), Elsevier and the MIT Press (1995).
M. Fellows: Transversals of vertex partitions in graphs, SIAM Journal of Disc. Math. 3 (1990), 206–215.
H. Fleischner and M. Stiebitz: A solution to a coloring problem of P. Erdős, Discrete Math. 101 (1992), 39–48.
F. Galvin: The list chromatic index of a bipartite multigraph, J. Combin. Theory Ser. B 63 (1995), 153–158.
P. Hall: On representation of subsets, J. London Math. Soc. 10 (1935), 26–30.
P. E. Haxell: A condition for matchability in hypergraphs, Graphs and Combinatorics 11 (1995), 245–248.
P. E. Haxell: A note on vertex list coloring, Combin. Probab. Comput. 10 (2001), 345–347.
P. E. Haxell: On the strong chromatic number, Comb. Prob. and Computing 13 (2004), 857–865.
P. E. Haxell: private communication.
R. Meshulam: The clique complex and hypergraph matching, Combinatorica 21(1) (2001), 89–94.
R. Meshulam: Domination numbers and homology, J. Combin. Theory Ser. A 102 (2003), 321–330.
R. Meshulam: private communication.
R. Yuster: Independent transversals in r-partite graphs, Discrete Math. 176 (1997), 255–261.
Author information
Authors and Affiliations
Corresponding author
Additional information
The research of the first author was supported by grant no 780/04 from the Israel Science Foundation, and grants from the M. & M. L. Bank Mathematics Research Fund and the fund for the promotion of research at the Technion.
The research of the third author was supported by the Sacta-Rashi Foundation.
Rights and permissions
About this article
Cite this article
Aharoni, R., Berger, E. & Ziv, R. Independent systems of representatives in weighted graphs. Combinatorica 27, 253–267 (2007). https://doi.org/10.1007/s00493-007-2086-y
Received:
Revised:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00493-007-2086-y