(Or “four colour theorem”) The theorem stating that if the plane is divided into connected regions which are to be coloured so that no two adjacent regions have the same colour (as when colouring countries on a map of the world), it is never necessary to use more than four colours.
The proof, due to Appel and Haken, attained notoriety by using a computer to check tens of thousands of cases and is thus not humanly checkable, even in principle. Some thought that this brought the philosophical status of the proof into doubt.
There are now rumours of a simpler proof, not requiring the use of a computer.
See also chromatic number
- Four colour theorem
four colour map theorem
[fawr-kawr-nerz, fohr-] /ˈfɔrˈkɔr nərz, ˈfoʊr-/ noun, (used with a singular or plural verb) Northern and Western U.S. 1. a place where roads cross at right angles; a crossroads. noun 1. a point in the SW U.S., at the intersection of 37° N latitude and 109° W longitude, where the boundaries of four states—Arizona, Utah, Colorado, […]
- Four-corner town
noun phrase A very small town; a crossroads: We were flabbergasted by these four-corner towns with four bars (1980s+)
[fawr-sahy-kuh l, fohr-] /ˈfɔrˌsaɪ kəl, ˈfoʊr-/ adjective 1. noting or pertaining to an internal-combustion engine in which a complete cycle in each cylinder requires four strokes, one to draw in air or an air-fuel mixture, one to compress it, one to ignite it and do work, and one to scavenge the cylinder. adjective 1. (US […]