public static DaThuc operator -(DaThuc f, DaThuc g)
        {
            DaThuc h      = new DaThuc();
            int    maxbac = Math.Max(f.n, h.n);

            h.n = maxbac;
            for (int i = 0; i <= h.n; i++)
            {
                h.dt[i] = f.dt[i] - g.dt[i];
            }
            return(h);
        }
        static void Main(string[] args)
        {
            DaThuc dt1 = new DaThuc();
            DaThuc dt2 = new DaThuc();

            dt1.Nhap();
            dt1.xuat();

            dt2.Nhap();
            dt2.xuat();

            Console.WriteLine("Toan tu +, - ");
            DaThuc dt3 = new DaThuc();

            dt3 = dt1 + dt2;
            dt3.xuat();
            dt3 = dt1 - dt2;
            dt3.xuat();
        }