def locate(tlsToFind, sets):
    """return
        - the set in which the given traffic light exists
        - the pair in which it was found
        - the index within the pair
        """
    for s in sets:
        for pair in s:
            if tlsToFind == pair.otl:
                return s, pair, 0
            elif tlsToFind == pair.tl:
                return s, pair, 1
    return None, None, None