void photonexchange()
{
   //
   // Draws the feynman diagrams for D0->mu+mu- via Rp violating SUSY.
   //
   TCanvas *c1 = new TCanvas("c1", "A canvas", 10, 10, 700, 600);
   c1->Range(0, 0, 60, 50);
   Int_t linsav = gStyle->GetLineWidth();
   gStyle->SetLineWidth(3);
   TLatex t;
   t.SetTextAlign(22);
   t.SetTextSize(0.1);
   TLine * l;
   //
   // The ee --> ee diagram
   //
   l = new TLine(10, 10, 50, 10); l->Draw();
   l = new TLine(10, 40, 50, 40); l->Draw();
   g = new TCurlyLine(30, 10, 30, 40, 0.08, 0.02); g->SetWavy(); g->Draw();
   //   g = new TCurlyArc(30, 10, 30, 40, 0.05, 0.02); g->Draw();
   t.DrawLatex(7,10,"e^{-}");
   t.DrawLatex(7,40,"e^{-}");
   t.DrawLatex(55,10,"e^{-}");
   t.DrawLatex(55,40,"e^{-}");
   t.DrawLatex(35,25,"#gamma");
   /*   //
   // The crossed diagram
   //
   l = new TLine(80, 10, 100, 10); l->Draw();
   l->SetLineStyle(1); // dashed line
   l = new TLine(80, 40, 100, 40); l->Draw();
   l = new TLine(100, 10, 120, 40); l->Draw();
   l = new TLine(100, 40, 120, 10); l->Draw();
   l = new TLine(100, 10, 100, 40); l->Draw();
   l->SetLineStyle(2); // dashed line
   t.DrawLatex(77,10,"#bar{u}");
   t.DrawLatex(77,40,"c");
   t.DrawLatex(125,10,"#mu^{+}");
   t.DrawLatex(125,40,"#mu^{-}");
   t.DrawLatex(95,25,"#check{q}");
   */
   
   c1->Update();
   gStyle->SetLineWidth(linsav);
}