\[\int^{\infty}_{0}(f(x))^{2}\,\mathrm{d}x=\frac{1}{2\pi}\int^{\infty}_{-\infty}%
{\left|\mathscr{M}\mskip-3.0muf\mskip 3.0mu\left(\tfrac{1}{2}+\mathrm{i}t%
\right)\right|}^{2}\,\mathrm{d}t.\]