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An equivalent definition of Seymour graphs is that the minimum size of a [[T-join]] equals the maximum number of edge-disjoint [[T-join|T-cuts]] for every node set ''T'' of even size. A co-NP characterization of Seymour graphs is known, see Ageev, Kostochka and Szigeti <ref>A. Ageev, A. Kostochka, Z. Szigeti, ''A Characterization of Seymour Graphs'', Journal of Graph Theory, 24/4 (1997), 357-364. [http://dx.doi.org/10.1002/(SICI)1097-0118(199704)24:4%3C357::AID-JGT8%3E3.0.CO;2-N DOI link], [http://www.g-scop.inpg.fr/~szigetiz/articles/aksz.pdf Author link].</ref>, and Ageev, Sebő and Szigeti <ref>A. Ageev, A. Sebő, Z. Szigeti, ''An excluded minor characterization of Seymour graphs'', Proc. 14th IPCO Conference, Lausanne (2010 to appear).</ref>.