Chebyshev's theorem

Etymology
From, the discoverer.

Proper noun
\frac{cx}{\ln x} <= \pi(x) <= \frac{Cx}{\ln x}$$
 * 1) The theorem that the prime counting function is of the same order of magnitude as x / ln x, i.e., for the prime counting function π, there are positive constants c and C such that:
 * $$\forall x\in\mathbb{N}:
 * 1) Bertrand's postulate, as proven by Chebyshev.
 * 2) Chebyshev's inequality.