his statement was completely proven by pafnuty chebyshev in 1850. for this reason, the postulate is also called the bertrand-chebyshev theorem or chebyshev's theorem. srinivasa ramanujan gave a simpler proof. ramanujan later used that proof when he discovered ramanujan primes. in 1932, paul erdős published a simpler proof using the chebyshev function θ("x").