Every planar map is four colorable
K. I. Appel, Wolfgang Haken · Bulletin of the American Mathematical Society · 1976
The following theorem is proved.THEOREM .Every planar map can be colored with at most four colors. AMS (MOS) subject classifications (1970). Primary05C15. 1 This work appears in full in two papers, Every planar map is four colorable; part I, Discharging, by K. Appel and W. Haken and part II, Reducibility, by K. Appel, W. Haken,