= \sum\limits_{k \in \mathbb{Z}} {\int_{ - \infty }^z {\frac{{f_Y \left( {k\pi + \arctan x} \right)}}
{{1 + y^2 }}dy} } \mathop = \limits^{{\text{L - MON}}} \int_{ - \infty }^z {\sum\limits_{k \in \mathbb{Z}} {\frac{{f_Y \left( {k\pi + \arctan y} \right)}}
{{1 + y^2 }}} dy} \Rightarrow