In the corner group, (RFU)^5 exchanges corners fur and bur. I only
mention this because of all the tools I use, it is the only one that
involves a lot of repetition. It's a fossil from my earliest cube
solution, c. 1980, which used _only_ repetitive processes.
(RFU)^5 is only useful to me because I solve corners first.
One-face-first solvers will find this incomprehensible.