Summary
A two-packing of a graph G is a bijection σ : V (G)↦V (G) such that for every two adjacent vertices a, b ∈ V (G) the vertices σ(a) and σ(b) are not adjacent. It is known [2, 6] that every forest G which is not a star has a two-packing σ. If F σ is the graph whose vertices are the vertices of G and in which two vertices a, b are adjacent if and only if a, b or σ − 1(a), σ − 1(b) are adjacent in G then it is easy to see that the chromatic number of F σ is either 1, 2, 3 or 4. We characterize, for each number n between one and four all forests F which have a two-packing σ such that F σ has chromatic number n.
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Notes
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Supported by NSERC of Canada Grant # 691325.
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Wang, H., Sauer, N. (2013). The Chromatic Number of the Two-Packing of a Forest. In: Graham, R., Nešetřil, J., Butler, S. (eds) The Mathematics of Paul Erdős II. Springer, New York, NY. https://doi.org/10.1007/978-1-4614-7254-4_12
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