@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},
}