1. Planar permutation graphs;Chartrand;Ann. Inst. H. Poincaré Sect. B,1967
2. Planar permutation graphs;Harary,1969
3. Acyclic colorings of planar graphs;Grünbaum;Israel J. Math.,1973
4. On acyclic coloring of the planar graphs;Kostochka,1974
5. also A.V. Kostochka, Acyclic 6-coloring of planar graphs, Diskret. Analiz., to appear (in Russian).