1. On a problem of P. Erdős;Altman;The American Math. Monthly,1963
2. Research problems in discrete geometry;Brass,2005
3. On the graph of large distances;Erdős;Discrete Comput. Geom.,1989
4. H. Hopf, E. Pannwitz: Aufgabe Nr. 167, Jahresbericht Deutsch. Math.-Verein. 43 (1934) p. 114.
5. On large distances in planar sets;Vesztergombi;Discrete Math.,1987