def state(T, Tg, Tm, Tv):
    """ return the state of a material at temp T, given its Tg, Tm, Tv """
    assert Tg < Tm < Tv , "wrong input"

    if T>=Tv:
        return "gas"
    elif T>=Tm:
        return "liquid"
    elif T>=Tg:
        return "rubbery solid"
    else:
        return "glassy solid"