 In his 1967 paper, "Disjointness in ergodic theory, minimal sets, and a problem in Diophantine approximation", Furstenberg introduced the notion of ‘disjointness,’ a notion in ergodic systems that is analogous to coprimality for integers.The notion turned out to have applications in areas such as number theory, fractals, signal processing and electrical engineering.In his 1977 paper, "Ergodic behavior of diagonal measures and a theorem of Szemerédi on arithmetic progressions", Furstenberg used methods from ergodic theory to prove a celebrated result by Endre Szemerédi, which states that any subset of integers with positive upper density contains arbitrarily large arithmetic progressions.