Rado's theorem is a theorem from the branch of mathematics known as Ramsey theory. It is named for the German mathematician Richard Rado. It was proved in his thesis, Studien zur Kombinatorik.
Let
Rado's theorem states that a system
- s1 = 0
- for all i ≥ 2, si can be written as a rational linear combination of the cj's in the Ck with k < i.
Folkman's theorem, the statement that there exist arbitrarily large sets of integers all of whose nonempty sums are monochromatic, may be seen as a special case of Rado's theorem concerning the regularity of the system of equations
where T ranges over each nonempty subset of the set {1, 2, ..., x}.
Other special cases of Rado's theorem are Schur's theorem and Van der Waerden's theorem.