static void Swap(DuetInTour x, DuetInTour y)
        {
            var t = x;

            x = y;
            y = t;
        }
        ///////////////////////////////////

        public int Compare(DuetInTour o1, DuetInTour o2)
        {
            if (o1.mark > o2.mark)
            {
                return(1);
            }
            else if (o1.mark < o2.mark)
            {
                return(-1);
            }

            return(0);
        }