<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def on_notebook_tab_switch(self, notebook, page, page_num, title_label, window, notebook_identifier):
 """Triggered whenever a left-bar notebook tab is changed. Updates the title of the corresponding notebook and updates the title of the left-bar window in case un-docked. :param notebook: The GTK notebook where a tab-change occurred :param page_num: The page number of the currently-selected tab :param title_label: The label holding the notebook's title :param window: The left-bar window, for which the title should be changed :param notebook_identifier: A string identifying whether the notebook is the upper or the lower one """

        title = gui_helper_label.set_notebook_title(notebook, page_num, title_label)
        window.reset_title(title, notebook_identifier)
        self.on_switch_page_check_collapse_button(notebook, page_num)