sS commonSuffix(S a, S b) {
  int i = 0, nb = b.length(), na = a.length(), n = min(na, nb);
  while (i < n && a.charAt(na-1-i) == b.charAt(nb-1-i))
    ++i;
  return i == nb ? b : substring(a, na-i);
}

sS commonSuffix(Iterable<S> l) {
  ret commonSuffixMulti(l);
}