TY  - BOOK
AU  - Appel,Kenneth
AU  - Haken,Wolfgang
TI  - Every planar map is four colorable
T2  - (Contemporary Mathematics ; )
SN  - 0821851039
AV  - QA612.18 A67 1989 
PY  - 1989///
CY  - Providence
PB  - Rhode Island American Mathematical society, 
KW  - Lemb
KW  - Problemas de los cuatro colores
ER  -