Thank you! I understood that. I think *g*.

I don't remember frilly surfaces from maths O Level (actually, I remember nothing from maths O Level, in which I scraped a grade C *g*).

And I second philmophlegm's call for a wider use of "on a frilly surface, all bets are off." We're going for our work Christmas lunch today. I fully intend to wow people with it (and I did try to explain your crochet book to a colleague the other day!)