“…To keep the discriminant of this algebra of the form 2 α 3 β 5 γ , a necessary and sufficient condition is that τ can be written in the form −ax p /cz r with ax p + by q + cz r = 0, a, b, c integers with all prime factors in {2, 3, 5}, and x, y, z integers. Here (p, q, r) is (3,2,15) for the first cover and (4, 2, 15) for the second.…”