There are questions and problems around us that even a grade school pupil can understand, but answering or solving them would take decades or perhaps centuries even for the greatest minds of the world. István Pink, a researcher at the University of Debrecen, and his Japanese colleague Takafumi Miyazaki, have found an answer to a question just like that, which has been open for 30 or 40 years. Their solution was published in one of the world’s most respected and celebrated journals in its field, the American Journal of Mathematics.