def ort_tag_categories(reisende):
    """Returns all location-day tuples in reisende.
    
    A location-day is the tuple:
    (line: str, direction: int, station: str, day: int)
    """
    ort_tag = reisende[["Linie", "Richtung", "Haltestelle", "Tag"]].itertuples(
        index=False, name=None
    )
    ort_tag = list(set(ort_tag))
    return ort_tag