@article{ZNSL_2011_391_a6,
     author = {G. V. Nenashev},
     title = {An upper bound on the chromatic number of circle graphs without $K_4$},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {149--156},
     publisher = {mathdoc},
     volume = {391},
     year = {2011},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_2011_391_a6/}
}