\begin{definition}[Definition:Riemann Zeta Function/Critical Line]
Consider the Riemann zeta function $\map \zeta s$.
Let $s = \sigma + i t$.
The line defined by the equation $\sigma = \dfrac 1 2$ is known as the '''critical line'''.
Hence the popular form of the statement of the Riemann Hypothesis:
:''All the nontrivial zeroes of the Riemann zeta function lie on the '''critical line'''.''
:520px
\end{definition}