private void subOp2ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            if (f3 == null)
            {
                f3 = new f3();
                f3.Show();
                f3.Owner = this;
                //f3.FormClosed += new FormClosedEventHandler(HacerLuegoDeCerrarF3);

                f3.FormClosed += HacerLuegoDeCerrarF3;
            }
            else
            {
                f3.Activate();
            }
        }
 public void HacerLuegoDeCerrarF3(object sender, EventArgs e)
 {
     f3 = null;
 }