@book {MR0349461, AUTHOR = {Ringel, Gerhard}, TITLE = {Map color theorem}, NOTE = {Die Grundlehren der mathematischen Wissenschaften, Band 209}, PUBLISHER = {Springer-Verlag}, ADDRESS = {New York}, YEAR = {1974}, PAGES = {xii+191}, MRCLASS = {05C15 (55A15)}, MRNUMBER = {0349461 (50 \#1955)}, MRREVIEWER = {H. V. Kronk}, BOEKCODE = {05C10}, }