The angular properties described above follow immediately from the functional form of the parabolas. The parabolas are reflected at the "a"-axis at "a" = 2"n", and the derivative of "b" with respect to "a" at this point is –1; hence the incidence angle is 45°. Since the clusters, like all triples, are repeated at integer multiples, the value 2"n" also corresponds to a cluster. The corresponding parabola intersects the "b"-axis at right angles at "b" = 2"n", and hence its reflection upon interchange of "a" and "b" intersects the "a"-axis at right angles at "a" = 2"n", precisely where the parabola for "n" is reflected at the "a"-axis. (The same is of course true for "a" and "b" interchanged.)