gistfile1.txt

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{arrows}

\begin{document}

\begin{tikzpicture}[scale=2.3]
\node (1) at (-0.77,0.5) {$1$};
\node (NL) at (0,1) {$N$};
\node (NR) at (1,1) {$N$};
\node (AL) at (0,0) {$A$};
\node (AR) at (1,0) {$A$};

\path[->, font=\scriptsize]
  (1) edge node[above left]{$0$} (NL)
  (1) edge node[below left]{$a$} (AL)
  (NL) edge node[above]{$S$} (NR)
  (AL) edge node[above]{$f$} (AR)
;

\path[dotted,->, font=\scriptsize]
  (NL) edge node[right]{$h$} (AL)
  (NR) edge node[right]{$h$} (AR)
;

\end{tikzpicture}

\end{document}