1. Finding an independent set in a planar graph;Albertson, Michael O.,1974
2. A lower bound for the independence number of a planar graph;Albertson, Michael O.;J. Combinatorial Theory Ser. B,1976
3. $\mu_{B}$;Berge, Claude,1987
4. Solution of the Heawood map-coloring problem;Ringel, Gerhard;Proc. Nat. Acad. Sci. U.S.A.,1968