Unfortunately, there is a simple but serious error in the final step of the proof.
Here is a simple direct proof.
This strikingly simple proof was discovered by J. Dixon.
It is useful to consider some rather simple examples to gain some intuition.
Although the idea is simple, its implementation is complicated by the fact that ......
In fact, the computation for $A$ becomes somewhat simpler.
We remark that this proof seems conceptually and calculationally simpler.
We first prove the (rather simpler) Theorem 7, by effecting a quite general reduction of the problem to the study of certain isotropy factors.
The simplest example of this is furnished by ......