four colour map theorem

four colour map theorem

(mathematics, application)(Or "four colour theorem") Thetheorem stating that if the plane is divided into connectedregions which are to be coloured so that no two adjacentregions have the same colour (as when colouring countries on amap of the world), it is never necessary to use more than fourcolours.

The proof, due to Appel and Haken, attained notoriety by usinga computer to check tens of thousands of cases and is thus nothumanly checkable, even in principle. Some thought that thisbrought the philosophical status of the proof into doubt.

There are now rumours of a simpler proof, not requiring theuse of a computer.

See also chromatic number