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J. Math. 21 (1977), 429-567.

K. Appel/W. Haken: Every planar map is four colourable.
AMS 1989, 740p. Pds. 64.

H. Bigalke: Heinrich Heesch. Kristallgeometrie, Parkettierungen, 
Vierfarbenforschung. Birkhaeuser 1988, 320p. DM 78.

Rudolf Fritsch/Gerda Fritsch: Der Vierfarbensatz.
Bibl. Inst. 1994, 200p. 3-411-15141-2. DM 30.

20818 Georges Gonthier: Formal proof - the four color theorem.
Notices AMS December 2008, 1382-1393.

Heinrich Heesch: Untersuchungen zum Vierfarbenproblem.
Bibl. Inst. 1969.

Joan Hutchinson: Coloring ordinary maps, maps of empires, and maps
of the Moon. Math. Magazine 66/4 (1993), 211-225.

T. Jensen/B. Toft: Graph coloring problems. Wiley 1995.
An account of more than 200 open colouring problems with comments and
references.

Oystein Ore: The four colour problem. Academic Press 1967.

9949 Gerhard Ringel: Fa''rbungsprobleme auf Fla''chen und Graphen.
Vlg. d. Wiss. 1959.

G. Ringel: Map colour theory. 1974.

G. Ringel/J. Youngs: Solution of the Heawood map-colouring problem.
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P. Tait: Note on a theorem in the geometry of position.
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Robin Thomas: An update of the four-color theorem.
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A new, simplified proof of the four-color theorem was published in 1997.

Klaus Wagner: Bemerkungen zum Vierfarbenproblem.
Jber. DMV 46 (1936), 26-32.

Klaus Wagner: U''ber eine Eigenschaft der ebenen Komplexe.
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Robert Wilson: Graphs, colourings and the four-colour theorem.
Oxford UP 2002, 160p. Pds 20 (pb).

15787 Robin Wilson: Four colours suffice.
EMS Newsletter December 2002, 15-19.