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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 process_docstring(app, what, name, obj, options, lines):
 """ Process the docstring for a given python object. Note that the list 'lines' is changed in this function. Sphinx uses the altered content of the list. """

    result = [re.sub(r'U\{([^}]*)\}', r'\1',
                     re.sub(r'(L|C)\{([^}]*)\}', r':py:obj:`\2`',
                            re.sub(r'@(' + '|'.join(FIELDS) + r')', r':\1',
                                   l)))
              for l in lines]
    lines[:] = result[:]