code: @Override
    public boolean retainAll(IntSet c)
    {
      modCount++;
  
      if (isEmpty() || c == this) {
        return false;
      }
      if (c == null || c.isEmpty()) {
        clear();
        return true;
      }
  
      ConciseSet other = convert(c);
      if (other.size == 1) {
        if (contains(other.last)) {
          if (size == 1) {
            return false;
          }
          return replaceWith(convert(other.last));
        }
        clear();
        return true;
      }
  
      return replaceWith(performOperation(other, Operator.AND));
    }
docs: {@inheritDoc}