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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def set_of_vars(arg_plot):
 """Build set of needed variables. Args: arg_plot (str):
 string with variable names separated with ``,``. Returns: set of str: set of variables. """

    return set(var for var in arg_plot.split(',') if var in phyvars.PLATES)