\begin{figure}[H]
  \begin{center}
    \unitlength=4pt
    \begin{picture}(60, 16)(0,-8)
    \gasset{Nw=5,Nh=5,Nmr=2.5,curvedepth=0}
    \thinlines
    \gasset{curvedepth=0,Nw=5,Nh=5}
    \node[Nmarks=i,iangle=180](A1)(0,0){$1$}
    \node(A2)(15,0){$2$}
    \node[Nmarks=f,fangle=270](A3)(30,0){$3$}
    \node(A4)(45,0){$4$}
    \node[Nmarks=f,fangle=270](A5)(60,0){$5$}
    \drawloop(A1){$b$}
    \drawedge(A1,A2){$a$}
    \drawedge(A2,A3){$b$}
    \drawedge[curvedepth=6](A3,A1){$a$}
    \drawedge(A3,A4){$b$}
    \drawedge[curvedepth=-6,ELside=r](A4,A2){$b$}
    \drawedge(A4,A5){$a$}
  \end{picture}
  \end{center}
  \caption{Un automate déterministe.}
\end{figure}