1. O. V. Borodin, “A Proof of Grunbaum’s Conjecture on the Acyclic 5-Colorability of Planar Graphs,” Dokl. Akad. Nauk SSSR 231, 18–20 (1976) [Sov.Math. Dokl. 17(1976), 1499–1502 (1977)].
2. O. V. Borodin, “Acyclic 3-Choosability of Planar Graphs without Cycles of Length from 4 to 12,” Diskretn. Anal. Issled. Oper. 16(5), 26–33 (2009) [J. Appl. Indust. Math. 4 (2), 158–162 (2010)].
3. O. V. Borodin, “Acyclic 4-Colorability of Planar Graphs without Cycles of Length 4 or 6,” Diskretn. Anal. Issled. Oper. 16(6), 3–11 (2009) [J. Appl. Indust. Math. 4 (4), 490–495 (2010)].
4. A. V. Kostochka, “Acyclic 6-Coloring of Planar Graphs,” Diskret. Analiz 28, 40–56 (1976).
5. H. L. Abbott and B. Zhou, “On Small Faces in 4-Critical Graphs,” Ars Comb. 32, 203–207 (1991).