private void button5_Click(object sender, EventArgs e)
        {
            btnMat2 lv2 = new btnMat2();

            lv2.Show();
            this.Close();
        }
        //int index;
        //int[] ListIndexDaDung;
        //int indexdadung;

        private void btncaudung_Click(object sender, EventArgs e)
        {
            //ListIndexDaDung = new int[3];
            btnMat2 mat2 = new btnMat2();

            mat2.Show();
            this.Close();
        }