Corollaries
Adding non-disjoint events:
\[ \mathbb{P}[A \cup B] = \mathbb{P}[A] +\mathbb{P}[B] - \mathbb{P}[A\cap B] \]
Union bound: \[ \mathbb{P}[A \cup B] \leq \mathbb{P}[A] +\mathbb{P}[B]\\ \] The union bound is frequently used for analyzing problems where the intersection is difficult to evaluate (e.g. multiple hypothesis testing)