Four Colors Suffice: How the Map Problem Was Solved - Revised Color Edition

On October 23, 1852, Professor Augustus De Morgan wrote a letter to a colleague, unaware that he was launching one of the most famous mathematical conundrums in history—one that would confound thousands of puzzlers for more than a century. This is the amazing story of how the "map problem" was solved.


The problem posed in the letter came from a former student: What is the least possible number of colors needed to fill in any map (real or invented) so that neighboring counties are always col...