private void BorrowWin_FormClosing(object sender, FormClosingEventArgs e)
 {
     if (this.Owner != null)
     {
         MainWin mainw = (MainWin)this.Owner;
         mainw.Show();
     }
 }
 private void button2_Click(object sender, EventArgs e)
 {
     if (this.Owner != null)
     {
         MainWin mainw = (MainWin)this.Owner;
         mainw.Show();
     }
     this.Close();
 }