This is from a conference talk that I gave about the classical Ramsey number R(3,3,3,3) at the XV Congreso Nacional de Matemáticas, Sociedad Colombiana de Matemáticas, Bogotá, Colombia, Summer 2005. (There is an error on the board. Can you find it?)Mr and Mrs "Ramsey", in the mountains west of Cali, Colombia. You can still see a part of Cali nestled between the mountains in the background.
