\begin{figure}[H]
  \begin{center}
    \unitlength=4pt
    \begin{picture}(60, 33)(0,-3)
    \gasset{Nw=5,Nh=5,Nmr=2.5,curvedepth=0}
    \thinlines
    \node[Nmarks=i,iangle=180](A1)(40,20){$1$}
    \node(A2)(60,20){$2$}
    \node[Nmarks=f,fangle=270](A3)(60,0){$3$}
    \node(A4)(0,20){$4$}
    \node(A5)(20,20){$5$}
    \node[Nmarks=i,iangle=270](A6)(20,0){$6$}
    \node[Nmarks=f,fangle=0](A7)(40,0){$7$}
    \drawedge(A1,A2){$a$}
    \drawedge(A3,A1){$b$}
    \drawedge(A6,A4){$a,b$}
    \drawedge(A5,A6){$a,b$}
    \drawedge(A6,A7){$a,b$}
    \drawloop[loopangle=90](A1){$b$}
    \drawloop[loopangle=90](A4){$a,b$}
    \gasset{curvedepth=4}
    \drawedge(A2,A3){$b$}
    \drawedge(A3,A2){$a$}
    \end{picture}
  \end{center}
  \caption{Un automate non émondé.}
\end{figure}