N, S

W, E

$\begin{array}{l}S\to N\\ N\to S\end{array}$

$\begin{array}{l}W\to W\\ E\to E\end{array}$

$\begin{array}{l}W\to W\\ E\to E\end{array}$

$\begin{array}{l}W\to W\\ E\to E\end{array}$