code: def _adjust_overlap(positions_list, index, direction):
      '''Increase overlap to the right or left of an index.
  
      :param positions_list: list of overlap positions
      :type positions_list: list
      :param index: index of the overlap to increase.
      :type index: int
      :param direction: which side of the overlap to increase - left or right.
      :type direction: str
      :returns: A list of overlap positions (2-element lists)
      :rtype: list
      :raises: ValueError if direction isn't \'left\' or \'right\'.
  
      '''
      if direction == 'left':
          positions_list[index + 1] -= 1
      elif direction == 'right':
          positions_list[index] += 1
      else:
          raise ValueError('direction must be \'left\' or \'right\'.')
      return positions_lisf _adjust_overlap(positions_list, index, direction):
      '''Increase overlap to the right or left of an index.
  
      :param positions_list: list of overlap positions
      :type positions_list: list
      :param index: index of the overlap to increase.
      :type index: int
      :param direction: which side of the overlap to increase - left or right.
      :type direction: str
      :returns: A list of overlap positions (2-element lists)
      :rtype: list
      :raises: ValueError if direction isn't \'left\' or \'right\'.
  
      '''
      if direction == 'left':
          positions_list[index + 1] -= 1
      elif direction == 'right':
          positions_list[index] += 1
      else:
          raise ValueError('direction must be \'left\' or \'right\'.')
      return positions_list
docs: Increase overlap to the right or left of an index.
  
      :param positions_list: list of overlap positions
      :type positions_list: list
      :param index: index of the overlap to increase.
      :type index: int
      :param direction: which side of the overlap to increase - left or right.
      :type direction: str
      :returns: A list of overlap positions (2-element lists)
      :rtype: list
      :raises: ValueError if direction isn't \'left\' or \'right\'.