Difficult math
==============


.. math::

  i \hbar \frac{\partial}{\partial t} \left( \begin{array}{c}
  \Psi^L \\
  \Psi^S \end{array} \right) = c  \left( \begin{array}{c}
  (\vec{\sigma} \cdot \vec{\pi}) \Psi^S \\
  (\vec{\sigma} \cdot \vec{\pi}) \Psi^L \end{array} \right)
  + m_ec^2  \left( \begin{array}{c}
   \Psi^L \\
  -\Psi^S \end{array} \right) + V  \left( \begin{array}{c}
  \Psi^L \\
  \Psi^S \end{array} \right)