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\begin{align}&\color{#66f}{\large\int_{0}^{1}{x^{-a} - x^{a} \over 1 - x}\,\dd x}
=\int_{0}^{1}{1 - x^{a} \over 1 - x}\,\dd x
-\int_{0}^{1}{1 - x^{-a} \over 1 - x}\,\dd x
=\Psi\pars{a + 1} - \Psi\pars{-a + 1}
\\[5mm]&=\bracks{\Psi\pars{a} + {1 \over a}} - \Psi\pars{1 - a}
={1 \over a} - \bracks{\Psi\pars{1 - a} - \Psi\pars{a}}
\\[5mm]&=\color{#66f}{\large{1 \over a} - \pi\cot\pars{\pi a}}\,,\qquad
\verts{\Re\pars{a}}\ <\ 1
\end{align}