I'm sorry, my 'rotation' was wrong -- as you point out, it would admit reflections. I'm glad to uncover this embarrassing bug, but on the other hand, oops. http

I'm sorry, my 'rotation' was wrong -- as you point out, it would admit reflections. I'm glad to uncover this embarrassing bug, but on the other hand, oops. https://en.wikipedia.org/wiki/Rotation_(mathematics) https://en.wikipedia.org/wiki/Rotation_(mathematics) has more lore to check against after I've done enough mental debugging.