M. van der Schel has come up with a very elegant move,
indeed. Easy to do, easy to think about. But he sets
no records. A 22-qtw diflip was reported some time
ago to this mailing list. It is true that the monoflip
takes only 10 qtw. Unfortunately, this does not allow you
to do a 20-qtw diflip, since the monoflip is only useful
as a tranform: in other words, when accompanied by its inverse.

Monoflip U Monoflip' U' still has 22 qtw. I suspect this to be
a minimum.

---Wechsler