\begin{figure}[H]
  \begin{center}
    \unitlength=4pt
    \begin{picture}(75, 6)(0,-1)
    \gasset{Nw=5,Nh=5,Nmr=2.5,curvedepth=0}
    \thinlines
    \node[Nmarks=i,iangle=180](A0)(0,0){$0$}
    \node(A1)(15,0){$1$}
    \node(A2)(30,0){$2$}
    \node(A3)(45,0){}     
    \node(Anm)(60,0){}      
    \node[Nmarks=f,fangle=0](An)(75,0){$n$}
    \drawedge(A0,A1){$a_1$}
    \drawedge(A1,A2){$a_2$}
    \drawedge(A2,A3){$a_3$}
     \put(50,0){$\ldots$}
    \drawedge(Anm,An){$a_n$}
    \end{picture}
  \end{center}
  \caption{Un automate reconnaissant $a_1\cdots a_n$.}
\end{figure}