\[f(x;\mu,\sigma^2) = \frac{1}{\sigma\sqrt{2\pi}}e^{-\frac{1}{2}\left(\frac{x-\mu}{\sigma}\right)^2}\]
$$
\begin{align}
\mbox{Union: } & A\cup B = \{x\mid x\in A \mbox{ or } x\in B\} \\
\mbox{Concatenation: } & A\circ B = \{xy\mid x\in A \mbox{ and } y\in B\} \\
\mbox{Star: } & A^\star = \{x_1x_2\ldots x_k \mid k\geq 0 \mbox{ and each } x_i\in A\} \\
\end{align}
$$
\[e^{i \pi} + 1 = 0\]