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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 tone_marks():
 """Keep tone-modifying punctuation by matching following character. Assumes the `tone_marks` pre-processor was run for cases where there might not be any space after a tone-modifying punctuation mark. """

    return RegexBuilder(
        pattern_args=symbols.TONE_MARKS,
        pattern_func=lambda x: u"(?<={}).".format(x)).regex