#!/usr/bin/env python
# coding: utf-8

# ```
# $$
# \begin{align}
# \sum_{k=1}^{\infty} \frac{1}{k^2} = \frac{\pi^2}{6}
# \end{align}
# $$
# ```

# $$
# \begin{align}
# \sum_{k=1}^{\infty} \frac{1}{k^2} = \frac{\pi^2}{6}
# \end{align}
# $$

# ```
# $$
# \newcommand{\rot}[1]{\nabla\times #1}
# \newcommand{\pdfrac}[2]{\frac{\partial #1}{\partial #2}}
# \begin{align}
#   \mathbf{D} &= 0 \\\
#   \mathbf{B} &= 0 \\\
#   \rot{\mathbf{E}} &= - \pdfrac{\mathbf{B}}{t} \\\
#   \rot{\mathbf{H}} &= \pdfrac{\mathbf{D}}{t}
# \end{align}
# $$
# ```

# $$
# \newcommand{\rot}[1]{\nabla\times #1}
# \newcommand{\pdfrac}[2]{\frac{\partial #1}{\partial #2}}
# \begin{align}
#   \mathbf{D} &= 0 \\\
#   \mathbf{B} &= 0 \\\
#   \rot{\mathbf{E}} &= - \pdfrac{\mathbf{B}}{t} \\\
#   \rot{\mathbf{H}} &= \pdfrac{\mathbf{D}}{t}
# \end{align}
# $$