"In mathematics, the four colour theorem, or the four colour map theorem, states that, given any separation of a plane into contiguous regions, producing a figure called a map, no more than four colour are required to colour the regions of the map so that no two adjacent regions have the same colour." -- Wikipedia

"A codebase composed of small interconnected modules that communicate with each other in a well-defined way will have a lower complexity than one where the modules communicate with each other haphazardly." - http://alexkudlick.com/blog/what-the-four-color-theorem-can-teach-us-about-writing-software/