<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def plot_title(ax, pretitle='', title='Figure', posttitle='', title_fontsize=14, title_arg=None):
 """Set title options of a matplotlib plot Args: ax: matplotlib axes pretitle(str):
 String to include before the general title of the figure posttitle (str):
 String to include after the general title of the figure title (str):
 Set the title for the figure title_fontsize (int):
 Defines the size of the title's font title_arg (dict):
 Addition arguments for matplotlib.title() call """

    current_title = ax.get_title()

    if not current_title:
        current_title = pretitle + title + posttitle

    title_arg = dict_if_none(title_arg)

    ax.set_title(current_title, fontsize=title_fontsize, **title_arg)