an:00866053
Zbl 0847.05050
O'Donnell, Paul
A 40-vertex \(4\)-chromatic triangle-free unit distance graph
EN
Geombinatorics 5, No. 1, 31-34 (1995).
1065-7371
1995
j
05C10 05C38 05C12
unit distance graph; plane
Paul ErdÃ¶s posed the question: are there any 4-chromatic subgraphs with no short cycles in the unit distance graph in the plane, that is, the graph whose vertices are all points in the real plane and whose edges connect all pairs of points distance 1 apart? The author constructs a 40-vertex 4-chromatic subgraph with no 3-cycles.
A.Tucker (Stony Brook)
0847.05049