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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(lovs):
 """Build set of variables from list. Args: lovs: nested lists of variables such as the one produced by :func:`list_of_vars`. Returns: set of str: flattened set of all the variables present in the nested lists. """

    return set(var for pvars in lovs for svars in pvars for var in svars)