public Form1()
    {
        InitializeComponent();
        Dictionary<char, string> dictionary = new Dictionary<char, string>();
        dictionary.Add('a', "%");
        dictionary.Add('A'," %");
        dictionary.Add('b', " &");
        dictionary.Add('B', " &");
        dictionary.Add('c', " <");
        dictionary.Add('C', " <");
    }

    private void button_Click(object sender, EventArgs e)
    {
        second_richtextbox=  (???)
    }