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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 field variables. Each var is a tuple, first component is a scalar field, second component is either: - a scalar field, isocontours are added to the plot. - a vector field (e.g. 'v' for the (v1,v2,v3) vector), arrows are added to the plot. Args: arg_plot (str):
 string with variable names separated with ``,`` (figures), and ``+`` (same plot). Returns: set of str: set of needed field variables. """

    sovs = set(tuple((var + '+').split('+')[:2])
               for var in arg_plot.split(','))
    sovs.discard(('', ''))
    return sovs