1. The imbedding of graphs in manifolds;Auslander;J. Math. Mech.,1963
2. Algebraic Topology: an Introduction;Massey,1967
3. Minimal imbeddings and the genus of a graph;Youngs;J. Math. Mech.,1963
4. A six colour problem;Franklin;J. Math. Phys.,1934
5. Blocks and the nonorientable genus of graphs;Stahl;J. Graph Theory,1977