def get_offset_map(doc, options):
    """Return mapping from original to cut document text offsets or None
    if the text is not cut."""
    if options.cut == 'tiab':
        # restrict to title and abstract
        sections = doc.text.split('\t')
        if len(sections) <= 2:
            return None
        else:
            tiab = '\t'.join(sections[:2])
            cut_text = doc.text[len(tiab):]
            offset_map = list(range(len(tiab))) + [None] * len(cut_text)
            return offset_map
    else:
        raise ValueError(options.cut)