\documentclass[12pt]{standalone}
\input{head}
\begin{document}
\begin{tikzpicture}\selectlanguage{english}
  \path (0,2) node(A) {$a$} (2,2) node(B) {$b$}
  (0,0) node(C) {$c$} (2,0) node(D) {$d$};
  \draw[->] (A) -- node[above]{$f$} (B);
  \draw[->] (B) -- node[right]{$h\circ g$} (D);
  \draw[->] (A) -- node[left]{$g\circ f$} (C);
  \draw[->] (C) -- node[below]{$h$} (D);
\end{tikzpicture}
\end{document}
%%% Local Variables:
%%% mode: latex
%%% TeX-master: t
%%% End: