\documentclass[12pt]{standalone}
\input{head}
\begin{document}
\begin{tikzpicture}\selectlanguage{english}
  \path (0,2) node(B){$b$} (2,2) node(UC){$Uc$} (4,2) node(C){$c$};
  \path                    (2,0) node(UX){$Ux$} (4,0) node(X){$x$};
  \draw[->] (B) -- node[above]{$u$} (UC);
  \draw[->] (B) -- node[left]{$f$} (UX);
  \draw[->,dotted] (UC) -- node[right]{$U\hat f$} (UX);
  \draw[->,dotted] (C) -- node[right]{$\hat f$} (X);
\end{tikzpicture}
\end{document}
%%% Local Variables:
%%% mode: latex
%%% TeX-master: t
%%% End: