[OS X TeX] oval-like arrow in XY-diagram

[delanoy at math.univ-lyon1.fr]

   Hello all,

 is there a tool in the XY-package (or some other LaTeX package) that
produces the same output (or almost the same) as the following :

\begin{document}
\setlength{\unitlength}{1cm}
\begin{picture}(12,3.5)
\put(1,2){A}
\put(1.4,2.1){\vector(1,0){1.5}}
\put(3,2){B}
\put(3.4,2.1){\vector(1,0){1.5}}
\put(5,2){C}
\put(3.2,1.8){\oval(3.8,1)[b]}
\put(5.1,1.75){\vector(0,1){0.1}}
\put(2,2.5){$f$}
\put(4,2.5){$g$}
\put(3,1){$f \circ g$}
\end{picture}
\end{document}

                              Thanks in advance,

                                            Ewan



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