// Simple test 

{
  TCanvas *canvas = new TCanvas("canvas", "my canvas", 600, 600);

  TF1 *fun = new TF1("fun", "x*x", -1, 1);
  fun->Draw();
  
  TLine *line1 = new TLine(-0.5, 0, -0.5, 1);
  TLine *line2 = new TLine(0, 0, 0, 1);
  TLine *line3 = new TLine(0.5, 0, 0.5, 1);

  // line1->Draw();
  // line2->Draw();
  // line3->Draw();

  for (auto *l : vector {line1, line2, line3}) {
    l->Draw();
  }

}