@article{RM_1972_27_3_a7,
     author = {\'E. G. Belaga},
     title = {A certain interpretation of the 4-coloring of a~planar graph},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     publisher = {mathdoc},
     volume = {27},
     number = {3},
     year = {1972},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/RM_1972_27_3_a7/}
}