Show that, for all $\theta \in \mathbb { R } \backslash 2 \pi \mathbb { Z }$, the series $\sum _ { n \geq 1 } \frac { e ^ { \mathrm { i } n \theta } } { n }$ converges.
Show that, for all $\theta \in \mathbb { R } \backslash 2 \pi \mathbb { Z }$, the series $\sum _ { n \geq 1 } \frac { e ^ { \mathrm { i } n \theta } } { n }$ converges.