static void Main1_3()
{
Phanso t1 = new Phanso();
Phanso t2 = new Phanso();
Console.WriteLine("Tong 2 phan so");
Phanso tTong = t1.Cong(t2); tTong.Hien();
Console.WriteLine("Hieu 2 phan so");
Phanso tHieu = t1.Tru(t2); tHieu.Hien();
}