====== PlayGround ======
\begin{equation}
   E_c = \frac{1}{2}mv^2
\end{equation}
\begin{equation}
   e^{i\theta} = \cos\theta + i\sin\theta
\end{equation}
<code bash>
#!/bin/bash
if [ $# -ne 1 ]; then
  echo "Usage: $0 <executable>"
  exit 1
fi
if [ -x $1 ]; then
  for i in 1 2 3 4; do
    scp $1 wolf0$i:$PWD/
  done
  exit 0
else
  echo "$1 isn't executable"
  exit 1
fi
</code>