Published online by Cambridge University Press: 24 October 2008
Let f(x, y) be a binary cubic form with real coefficients and determinant D ≠ 0. In a recent paper, Mordell has proved that there exist integral values of x, y, not both zero, for which
These inequalities are best possible, since they cannot be satisfied with the sign of strict inequality when f(x, y) is equivalent to
for the case D < 0, or to
for the case D > 0.
* The determinant of ax 3 + bx 2y + cxy 2 + dy 3 is the invariant
† Proc. London Math. Soc. (in course of publication).
* Proc. London Math. Soc. (2), 44 (1938), 412–31Google Scholar, and 45 (1939), 98–125.
* For references, see Koksma, , Diophantische Approximationen, p. 55Google Scholar. A much weaker result would suffice for the argument.
* See, for example, Perron, Kettenbrüchen, Kapitel 2, Satz 16.