The notation { } is quite correct. It just isn’t an atomic symbol for
the empty set but an expression consisting of the two characters “{”
and “}”, with a list (here, an empty list) of elements between them.
Reminds me of typographically composite stuff that has its own scalar
value ("code point") now:
:= is ≔
... is …
(Yes, they're different because they're semantically atomic, unlike { }.)
I was just browsing Bourbaki's "Éléments", and saw ∅ there. I wasn't
sure because Springer uses LaTeX for a lot of things now, which has both
\emptyset (producing something resembling the German variant, a
struck-through zero, though I know many of the German resources I looked
at didn't use LaTeX) and \varnothing (producing ∅). But this
Regarding the empty set, the page
http://jeff560.tripod.com/set.html
rather convincingly attributes the symbol to André Weil, who says that
it was inspired by the Norwegian letter “Ø”.
clarifies all.
Thx,
Stephan
