1. Erdős, P., Harary, F., Tutte, W.T.: On the dimension of a graph. Mathematika, London. 12, 118–122 (1965)
2. Hochberg, R., O’Donnell, P.: Some 4-chromatic unit-distance graphs without small cycles. Geombinatorics. V(4), 137–114 (1996)
3. Mycielski, J.: Sur le coloriage des graphes. Colloq. Math. 3, 161–162 (1955)
4. O’Donnell, P.: A triangle-free 4-chromatic graph in the plane. Geombinatorics. IV(1), 23–29 (1994)
5. O’Donnell, P.: A 40 vertex 4-chromatic triangle-free unit-distance graph in the plane. Geombinatorics. V(1), 30–34 (1995)