[FOM] Slashed circle symbol for the empty set

[Johanna Franklin]

Weil makes this claim in his autobiography _The Apprenticeship of a 
Mathematician_, but gives no explanation for why he chose that 
particular symbol.

p. 114: "Much later, my own part in these discussions earned me the 
respect of my daughter Nicolette, when she learned the symbol 
$\emptyset$ for the empty set at school and I told her that I had been 
personally responsible for its adoption. The symbol came from the 
Norwegian alphabet, with which I alone among the Bourbaki group was 
familiar."

Johanna Franklin

Howard, William A. wrote:
> Someone just told me that the empty set symbol resembling a slashed small
> circle was chosen from the Norwegian alphabet by Andre Weil. Does anyone
> know whether this is true, and, if so, why Weil chose this symbol?
> 
> In any case, I had always assumed that the use of this symbol was
> motivated by the idea that one wants a suggestive symbol for the "zero
> set"; but, of course, the "obvious" reason need not be the historical
> reason.
> 
> Bill Howard