@article{10_1090_S0894_0347_1992_1135027_1,
     author = {Thomassen, Carsten},
     title = {The even cycle problem for directed graphs},
     journal = {Journal of the American Mathematical Society},
     pages = {217--229},
     publisher = {mathdoc},
     volume = {05},
     number = {2},
     year = {1992},
     doi = {10.1090/S0894-0347-1992-1135027-1},
     url = {http://geodesic.mathdoc.fr/articles/10.1090/S0894-0347-1992-1135027-1/}
}