def merge_short_sentences(lst: list) -> list:
    """Merge subsequent sentences that consist of only a single word."""
    last_is_short = False
    out_lst = []
    for s in lst:
        if s.find(' ') == -1:
            if last_is_short:
                out_lst[-1] = out_lst[-1] + s
            else:
                last_is_short = True
                out_lst.append(s)
        else:
            last_is_short = False
            out_lst.append(s)
    return out_lst