We note that, although, in [Z], Chen
uses a slightly different model for the G-module, his module is
readily seen to be isomorphic to ours.
Translated into our setting,
Chen proves the following:
Thus, in order to prove Theorem 1.1, it will suffice
to establish that there are
no further G-orbits in than those listed in Table 1, and that
We shall however give a fully self-contained proof of Theorem 1.1.