1. Graph Theory with Applications;Bondy,1976
2. Solution of Ringel's problems on the vertex-face coloring of plane graphs and on the coloring of 1-planar graphs;Borodin;Diskret. Analiz,1984
3. Acyclic colouring of 1-planar graphs;Borodin;Discrete Applied Mathematics,2001
4. The structure of 1-planar graphs;Fabrici;Discrete Mathematics,2007
5. Ein Sechsfarbenproblem auf der Kugel;Ringel;Abh. Math. Sem. Univ., Hamburg,1965