1. 1) Ahuja, R. K., Magnanti, T. L., and Orlin, J. B., Network Flows: Theory, Algorithm, and Applications, Prentice Hall (1993).
2. 2) Arora, S., and Barak, B., Computational Complexity: A Modern Approach, Cambridge (2009).
3. 3) Bang-Jensen, J., ``Edge-disjoint in- and out-branchings in tournaments and related path problems,'' Journal of Combinatorial Theory, Series B, 51(1): 1-23 (1991).
4. 4) Bang-Jensen, J., and Gutin, G. Z., Digraphs: Theory, Algorithms and Applications, Springer, 2nd edition (2008).
5. 5) Bérczi, K., and Frank, A., Variations for Lovász' Submodular Ideas, In Grötschel, M., and Kotona, G. O. H., editors, Building Bridges: Between Mathematics and Computer Science, volume 19 of Bolyai Society Mathematical Studies, pp. 137-164, Springer (2008).