1. Network Flows;Ahuja,1993
2. Rings of sets;Birkhoff;Duke Math. J.,1937
3. Oriented Matroids;Björner,1993
4. E. Brehm, 3-orientations and Schnyder 3-tree-decompositions, Diplomarbeit, Freie Universität, Berlin, 2000.
5. Linear Programming and Extensions;Dantzig,1963