[see also: easy, straightforward, direct
Unfortunately, there is a simple but serious error in the final step of the proof.
The simplest example of this is furnished by......
Here is a simple direct proof.
This strikingly simple proof was discovered by J. Dixon.
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.