Assertion: dual graph | /r/CapableOf | extend to map
Facets:
value: by lothar heffter
type: OTHER
value: in 1891
type: TEMPORAL
value: on non-planar surfaces
type: LOCATION
Source sentences:
text: In connection with the four color theorem, the dual graphs of maps (subdivisions of the plane into regions) were mentioned by Alfred Kempe in 1879, and extended to maps on non-planar surfaces by Lothar Heffter [de] in 1891.