Изменения

<tex>PH_{1} = {\bigcup \atop {k i \in \mathbb{N}}} \Sigma_{i}</tex>.<br/><tex>PH_{2} = {\bigcup \atop {k i \in \mathbb{N}}} \Pi_{i}</tex>.<br/><tex>PH_{3} = {\bigcup \atop {k i \in \mathbb{N}}} (\Sigma_{i} \cup \Pi_{i})</tex>.