\documentclass[12pt]{standalone}
\input{head}
\begin{document}
\begin{tikzpicture}\selectlanguage{english}
  \path (0,2) node(IT){$S$} (2,2) node(TT){$\{S\}$};
  \path                            (2,0) node(T){$S$} node[below]{$\phantom{\mu}$};
  \tikzsquig (IT) -- node[above]{$\eta_{\power X}$} (TT);
  \tikzsquig (TT) -- node[right]{$\mu_X$} (T);
  \tikzsquig (IT) -- node[left]{$1_{\power X}$} (T);
\end{tikzpicture}
\end{document}
%%% Local Variables:
%%% mode: latex
%%% TeX-master: t
%%% End: