static L<File> conceptBackupFiles(S progID) {
  S regexp = "^(.*)\\.backup(20\\d\\d)(\\d\\d)(\\d\\d)-(\\d\\d)$";
  File dir = programDir(progID);
  new L<File> l;
  for (File f : listFilesNotDirs(dir, newFile(dir, "backups"))) {
    S s = f.getName();
    S originalName = regexpFirstGroup(regexp, s);
    continue unless eq(originalName, "concepts.structure.gz");
    l.add(f);
  }
  ret l;
}