public Roman Lower(Roman number)
        {
            Roman previous = null;
            foreach (Roman r in romans)
                if (r == number)
                    return previous;
                else
                    previous = r;

            return null;
        }
        public Roman Higher(Roman number)
        {
            bool isNext = false;
            foreach (Roman r in romans)
                if (isNext)
                    return r;
                else
                    if (r == number)
                        isNext = true;

            return null;
        }