who was a major figure in 19th-century mathematics and arguably the first modern mathematician because of his general, abstract approach to many problems. In geometry, he started the development of those tools which Einstein would eventually use to describe the universe and which in the 20th century would be turned into the theory of Riemannian manifolds. He did much significant work in analysis, in which his name is preserved in the Riemann integral, the Cauchy–Riemann equations, and Riemann surfaces. He also made connections between prime number theory and analysis: he formulated the Riemann hypothesis, a conjecture concerning the zeta function, which, if proved, would give information about the distribution of prime numbers.