[1]http://www.bbc.co.uk/programmes/b00w5675
루트 시스템 (root system)과 딘킨 다이어그램 (Dynkin diagram)
http://mathoverflow.net/questions/6139/how-can-i-learn-about-doing-linear-algebra-with-trace-diagrams
http://en.wikipedia.org/wiki/Trace_diagram
http://en.wikipedia.org/wiki/Penrose_graphical_notation