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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 _add_element(potential, var, potential_tag):
 """ Helper function to add variable tag to the potential_tag Parameters potential: dict Dictionary containing Potential data. For example: {'role': 'Utility', 'Variables': ['D0', 'D1', 'C0', 'C1'], 'type': 'Tree/ADD', 'UtilityVaribale': 'U1'} var: string New Element tag which needs to be added to the potential tag. For example: 'type' potential_tag: etree Element etree element which would contain potential tag For example: <Element Potentials at 0x7f315fc44b08> <Element Branch at 0x7f315fc44c88> <Element Branch at 0x7f315fc44d88> <Element Subpotentials at 0x7f315fc44e48> Examples -------- """

        if var in potential:
            etree.SubElement(potential_tag, var).text = potential[var]