> even seemingly innocent notation like {0, 1, 2, 3, ...} I think that would be OK. There is a fine line between having to define everything and just using the

> even seemingly innocent notation like {0, 1, 2, 3, ...} I think that would be OK. There is a fine line between having to define everything and just using the math and letting the reader pick up on their own. > set membership, as in if x,y ∈ N, then (x+y) ∈ N. Yeah that was non-sense. It definitely didn't belong so early on in the book. Several people emailed me about this and it has been fixed in print/pdf versions now. More on set notation: http://cnd.mcgill.ca/~ivan/miniref/set_notation.pdf http://cnd.mcgill.ca/~ivan/miniref/set_notation.pdf