A theorem similar to van der Waerden's theorem is "Schur's theorem": for any given "c" there is a number "N" such that if the numbers 1, 2, ..., "N" are coloured with "c" different colours, then there must be a pair of integers "x", "y" such that "x", "y", and "x"+"y" are all the same colour. Many generalizations of this theorem exist, including Rado's theorem, Rado–Folkman–Sanders theorem, Hindman's theorem, and the Milliken–Taylor theorem. A classic reference for these and many other results in Ramsey theory is Graham, Rothschild, Spencer and Solymosi, updated and expanded in 2015 to its first new edition in 25 years.