\begin{figure}[H]
  \begin{center}
    \unitlength=4pt
    \begin{picture}(30, 8)(0,-4)
    \gasset{Nw=5,Nh=5,Nmr=2.5,curvedepth=0}
    \thinlines
    \node[Nmarks=i,iangle=180](A3)(0,0){$3$}
    \node(A2)(15,0){$2$}
    \node[Nmarks=f,fangle=0](A1)(30,0){$1$}
    \put(78,6.2){$\cdots$}
    \drawedge(A2,A1){$a$}
    \gasset{curvedepth=3}
    \drawedge(A3,A2){$a$}
    \drawedge(A2,A3){$b$}
    \end{picture}
  \end{center}
  \caption{L'automate minimal du code préfixe $a(ba)^*a$.}
\end{figure}