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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 merge_next(letters: List[str], positions: List[int]) -> List[str]: """ Given a list of letter positions, merge each letter with its next neighbor. :param letters: :param positions: :return: ['ab', '', 'ov', '', 'o'] ['ab', '', 'ov', 'o', ''] """

    for pos in positions:
        letters[pos] = letters[pos] + letters[pos + 1]
        letters[pos + 1] = ""
    return letters