let mut to_download_ = HashSet::new();

                    to_download.push(CS::Change(h));

                    let h = CS::Change(h);
                    if to_download_.insert(h.clone()) {
                        to_download.push(h);
                    }

                    to_download.push(ch.clone());

                    if to_download_.insert(ch.clone()) {
                        to_download.push(ch.clone());
                    }