\begin{figure}[H]
  \begin{center}
    \unitlength=4pt
    \begin{picture}(40, 32)(0,0)
    \gasset{Nw=6,Nh=6,Nmr=3,curvedepth=0}
    \thinlines
    \gasset{Nw=6,Nh=6}
    \node[Nmarks=i,iangle=180](E)(0,32){$\emptyset$} 
    \node(CP)(15,32){$CP$} 
    \node(C)(30,32){$C$}
    \node(CLP)(20,22){$CLP$}
    \node(CPS)(40,22){$CPS$}
    \node(L)(20,10){$L$}
    \node(S)(40,10){$S$}
    \node(LPS)(30,0){$LPS$}
    \node(LS)(15,0){$LS$}
    \node[Nmarks=f,fangle=180](CLPS)(0,0){$\substack{CL\\PS}$}

    \drawedge(E,CP){$C$}    \drawedge(CP,E){}
    \drawedge(CP,C){$P$}    \drawedge(C,CP){}

    \drawedge[ELside=r](C,CLP){$L$}   \drawedge(CLP,C){}
    \drawedge[ELside=r](CLP,L){$C$}   \drawedge(L,CLP){}
    \drawedge[ELside=r](L,LPS){$S$}   \drawedge(LPS,L){}

    \drawedge(C,CPS){$S$}   \drawedge(CPS,C){}
    \drawedge(CPS,S){$C$}   \drawedge(S,CPS){}
    \drawedge(S,LPS){$L$}   \drawedge(LPS,S){}

    \drawedge(LPS,LS){$P$}  \drawedge(LS,LPS){}
    \drawedge(LS,CLPS){$C$} \drawedge(CLPS,LS){}
    \end{picture}
  \end{center}
  \caption{Une modélisation du problème.}
\end{figure}