\begin{figure}[H]
  \begin{center}
     \unitlength=4pt
     \begin{picture}(20, 12)(0,1)
     \gasset{Nw=5,Nh=5,Nmr=2.5,curvedepth=0}
     \thinlines
     \node[Nmarks=i,iangle=180,Nw=6,Nh=5,Nmr=3](A1)(0,0){$2,4$}
     \node[Nmarks=f,fangle=0,Nw=9,Nh=6,Nmr=3](A2)(20,0){$1,2,3,4$}
     \drawloop[loopangle=90](A2){$a,b$}
     \drawedge(A1,A2){$a$}
     \end{picture}
   \end{center}
   \caption{L'automate ${\cal A}^r$.}
\end{figure}