1. G. Ringel, Extremal Problems in the Theory of Graphs, Theory of Graphs and its Applications (Proc. Sympos. Smolenice, 1963), pp. 85–90. Publ. House Czechoslovak Acad. Sci., Prague, 1964.
2. M. Simonovits, Extremal graph problems with conditions, Combinatorial Theory and its Applications III, Colloquia Math. Soc. J. Bolyai, 4, North-Holland Publishing Co., Amsterdam-London, 1970, 999–1012.
3. V. T. Sós, P. Erdős and W. G. Brown, On the existence of triangulated spheres in 3-graphs, and related problems, Period. Math. Hung., 3 (1973), 221–228.
4. P. Turán, Research Problems, Magy. Tud. Akad. Mat. Kut. Int. Közl., 6 (1961), 417–423.