Talking about which ...
I confess I usually type a Danish Ø for convenience when I'm using this, though
for publication I would tend to substitute the proper ∅.
Whenever I saw the empty set symbol in printed math literature in
Germany, it closely resembled Ø; I don't think I ever saw a
struck-through circle ∅. (A similar difference: Set subtraction – in
Germany as well as the US – I've only ever seen with a backslash \ (or a
symbol looking like a slightly prolonged backslash) but never with a
Unicode-style ∖ at a 45° angle.) And below the university level Germans
write { }, which I like better.
I suspect that circular ∅ and ∖ at 45° are more recent symbols,
intentionally designed to look different from Ø and \. Does anyone know?
Stephan
