1. Brown, W.G., Erdős, P., Simonovits, M.: Extremal problems for directed graphs. J. Combin. Theory Ser. B 15, 77–93 (1973)
2. W.G. Brown, P. Erdős, M. Simonovits, Inverse extremal digraph problems, Finite and infinite sets, Vol. I, II (Eger, 1981), 119-156, Colloq. Math. Soc. János Bolyai, 37, North-Holland, Amsterdam, 1984
3. W.G. Brown and F. Harary, Extremal digraphs, Combinatorial theory and its applications, I (Proc. Colloq., Balatonfred, 1969), pp. 135-198. North-Holland, Amsterdam, 1970
4. W.G. Brown, M. Simonovits, Extremal multigraph and digraph problems, Paul Erdős and his mathematics, II (Budapest, 1999), 157-203, Bolyai Soc. Math. Stud., 11, János Bolyai Math. Soc., Budapest, 2002
5. Huang, Z., Lyu, Z.: 0–1 matrices with zero trace whose squares are 0–1 matrices. Linear Algebra Appl. 565, 156–176 (2019)