private void subOp1ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            if (f2 == null)
            {
                f2 = new f2();
                f2.Show();
                f2.Owner = this;
                //f2.FormClosed += new FormClosedEventHandler(HacerLuegoDeCerrarF2);

                f2.FormClosed += HacerLuegoDeCerrarF2;
            }
            else
            {
                f2.Activate();
            }
        }
 public void HacerLuegoDeCerrarF2(object sender, EventArgs e)
 {
     f2 = null;
 }