This continues from our planar graphs video with Maria Chudnovsky at https://www.youtube.com/watch?v=xBkTIp6ajAg More links & stuff in full description below ↓↓↓ Four color map theorem (video): https://www.youtube.com/watch?v=NgbK43jB4rQ The strong perfect graph theorem (paper): https://arxiv.org/abs/math/0212070 Professor Chudnovsky's webpage: https://web.math.princeton.edu/~mchudnov/ NUMBERPHILE Website: http://www.numberphile.com/ Numberphile on Facebook: http://www.facebook.com/numberphile Numberphile tweets: https://twitter.com/numberphile Numberphile is supported by the Mathematical Sciences Research Institute (MSRI): http://bit.ly/MSRINumberphile Videos by Brady Haran Support us on Patreon: http://www.patreon.com/numberphile Brady's videos subreddit: http://www.reddit.com/r/BradyHaran/ A run-down of Brady's channels: http://www.bradyharan.com/ Sign up for (occasional) emails: http://eepurl.com/YdjL9