private void добавитьОперациюToolStripMenuItem2_Click(object sender, EventArgs e)
{
if (f20 == null)
{
f20 = new Form20();
f20.MdiParent = this;
f20.FormClosed += new FormClosedEventHandler(f20_FormClosed);
f20.Show();
}
else
{
f20.Activate();
}
}
void f20_FormClosed(object sender, FormClosedEventArgs e)
{
f20 = null;
}