Tim wrote:

> Is the typo "of" instead of "off"? Or is it something else?

It should read "off" methinks. (The symmetry group **of** my shelf is the permutations :-) )

> It has often been helpful for me to structure my thoughts by imagining handling mathematical gadgets like something you can hold in your hand, that's why I use this metaphor (take a Lie group off the shelf, now you have a Lie group in your hand, what can you do with it etc.)

Yeah. I like that, too.