- 666

- 2

Used in context here http://books.google.com/books?id=4Y-ownk6ilsC&pg=PA70&lpg=PA70&dq=abraham+marsden+foundation+of+mechanics&source=bl&ots=KGabbhy6XM&sig=MNvhtxISRyHdHGC3waYvSZtd-qg&hl=en&ei=zOnKSfraKp_inQeShsjnCQ&sa=X&oi=book_result&resnum=1&ct=result top of the page.

I've previously seen the notation [tex]\bold{R}^2-\{\bold{0}\}[/tex] for the cartesian plane with the origin excluded, so I hesitated to assume that the above notation meant the same thing.