for(set<Object *>::const_iterator i=objects.begin(); i!=objects.end(); ++i)
if(!dynamic_cast<Track *>(*i) || (*i)->get_n_link_slots()!=2)
{
for(set<Object *>::const_iterator i=objects.begin(); i!=objects.end(); ++i)
if(!dynamic_cast<Track *>(*i) || (*i)->get_n_link_slots()!=2)
{