1. S.A. Burr, Subtrees of directed graphs and hypergraphs, in: Proceedings of the 11th Southeastern Conference on Combinatorics, Graph theory and Computing, I, Vol. 28, Florida Atlantic University, Boca Raton, FL, 1980, pp. 227–239.
2. Trees in tournaments;Häggkvist;Combinatorica,1991
3. Trees in tournament;Havet;J. Discrete Math.,2002
4. Median orders of tournaments;Havet;J. Graph Theory,2000
5. Ein kombinatorischer Satz;Rédei;Acta Litt. Szeged,1934