\[\lim_{\nu\to 0+}\frac{1}{2\pi\mathrm{i}}\left(\left\langle\left(\mu-\mathrm{i}%
\nu-T\right)^{-1}f,f\right\rangle-\left\langle\left(\mu+\mathrm{i}\nu-T\right)%
^{-1}f,f\right\rangle\right)\]