sS simplifySafetyTags(L<S> l) {
  if (l(l) > 1 && l.contains("safe"))
    ret listMinus(l, "safe");
  ret l;
}

sS simplifySafetyTags(S tags) {
  L<S> l = tokSplitAtComma(tags);
  L<S> l2 = simplifySafetyTags(l);
  ret l(l2) != l(l) ? joinWithComma(l) : tags;
}