Comment by crasshopper

For those who want to know more, this topic links nicely into A-D-E theory, Dynkin diagrams, and Coxeter groups.

https://www.youtube.com/playlist?list=PL-XzhVrXIVeSVcV9iRJ4S...

https://www.youtube.com/playlist?list=PL-XzhVrXIVeQ298S6uCyo...

http://math.ucr.edu/home/baez/week230.html

https://unapologetic.wordpress.com/category/geometry/root-sy...

http://www.math.harvard.edu/~lurie/papers/thesis.pdf

Beautiful world this author is peeking into. Enjoy.