Given a graph , the arboricity is the minimum number of edge-disjoint acyclic subgraphs (i.e., spanning forests) whose union is .
An acyclic graph therefore has .
It appears that a regular graph of vertex degree has arboricity
(1)
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Let be a nonempty graph on vertices and edges and let be the maximum number of edges in any subgraph of having vertices. Then
(2)
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(Nash-Williams 1961; Harary 1994, p. 90).
The arboricity of a planar graph is at most 3 (Harary 1994, p. 124, Problem 11.22).
The arboricity of the complete graph is given by
(3)
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and of the complete bipartite graph by
(4)
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(Harary 1994, p. 91), where is the ceiling function.