TY  - BOOK
AU  - Ore, Oystein
TI  - The four-color problem
T2  - Pure and Applied Mathematics, v. 27
U1  - 511.5 
PY  - 1968///
CY  - New York
PB  - Academic Press
N1  - "Discusses the methods in graph theory that have been developed in the last century"
ER  -