private void button2_Click(object sender, RoutedEventArgs e)
        {
            Plan p = new Plan();
            p = Parser.ParseXML(textBox1.Text);
            Plan p2 = p.ConsistentAccordance();

            //if plan has a consistent accordance,
            if (p2.HasOfferings())
            {
                MessageBox.Show("The plan has consistent accordance(s):\n" + p2.ToString());
            }
            else
            {
                MessageBox.Show("The plan has no consistent accordances.");
            }
        }