{
  gSystem.Load("libGeom");
  TGeoManager *geom = new TGeoManager("world","Studying materials");
  TGeoMaterial *mat = new TGeoMaterial("Vacuum",0,0,0);
  TGeoMedium   *med = new TGeoMedium("Vacuum",1,mat);
  TGeoVolume *top = geom->MakeBox("TOP",med,5.0,5.0,14.0);
  geom->SetTopVolume(top);
  TGeoVolume *revtyvek = geom->MakeBox("REVTYVEK",med,3.0,3.0,11.0);
  top->AddNode(revtyvek,1);
  TGeoVolume *crystal = geom->MakeBox("CRYSTAL",med,2.0,2.0,10.0);
  revtyvek->AddNode(crystal,1);
  geom->CloseGeometry();
  top->SetVisibility(kTRUE);
  top->SetLineColor(1);
  top->SetLineWidth(2);
  top->VisibleDaughters();
  revtyvek->SetVisibility(kTRUE);
  //  revtyvek->VisibleDaughters();
  revtyvek->SetLineColor(2);
  revtyvek->SetLineWidth(2);
  crystal->SetVisibility(kTRUE);
  crystal->SetLineColor(3);
  gGeoManager->SetVisOption(0);
  gGeoManager->SetTopVisible();
  gGeoManager->SetVisLevel(3);
  top->Draw();
}