static L<PairS> ai_findSuffixAddedElementsInSet(Set<S> set, S addedSuffix) {
  new L<PairS> out;
  for unnull (S s : set) {
    S x = s + addedSuffix;
    if (set.contains(x))
      addPair(out, s, x);
  }
  ret out;
}