I've always thought, albeit vaguely, that Z for the integers came earlier
than Bourbaki from German Zyklus or zyklisch, as in cyclic group. I can't
think of a comparable origin for Q, unless maybe from Latin quantum or a
related Latin word, as in "quantity" or "how much", perhaps meant to refer
to the fact that measurements made by physicists, chemists, engineers,
carpenters, etc., generally turn out to be rational numbers.
As for the null set, I don't recall now what symbol the Bourbakists used.
Was it a little square (or rectangle)? Or the Greek letter for what we
call "phi" (pronounced "fie" or "fee", according to your nationality or
native language)? Or what?
Gordon Fisher gfisher@shentel.net