def METHOD_NAME():
    x, y, z = Ob('x'), Ob('y'), Ob('z')
    f, g = Box('f', x, y), Box('g', y, z)
    with raises(AxiomError) as err:
        Arrow((g, ), x, y)
    with raises(AxiomError) as err:
        Arrow((f, ), x, z)
    with raises(AxiomError) as err:
        g >> f