@article{DM_1990_2_4_a4,
     author = {I. A. Muzychuk},
     title = {On the nonexistence of even 4-critical graphs of order~12},
     journal = {Diskretnaya Matematika},
     pages = {47--59},
     publisher = {mathdoc},
     volume = {2},
     number = {4},
     year = {1990},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DM_1990_2_4_a4/}
}