The symbol $\varnothing$ for the empty set was introduced by Bourbaki, inspired by the Norwegian alphabet $\varnothing.$ It has no relation with the Greek letter $\phi.$
From my schooldays, when the concept of the empty set was introduced, I found people pronouncing this symbol of the empty set as "Phi".
My questions are:
If the symbol has no connection with the Greek letter "Phi", then is it legitimate to call it "Phi"?
If not, what should we call the symbol $\varnothing$?
How is the Norwegian letter $\varnothing$ pronounced?
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$\begingroup$I'd read $A=\varnothing$ as $A$ is empty or $A$ is the empty set.
$\endgroup$ $\begingroup$Ø in Norwegian is pronounced somewhat similar to u in under or ea in early [1].
I think it is generally called "the empty set" and it is not acceptable to call it "phi".
[1]
$\endgroup$ 2 $\begingroup$I usually pronounce $\varnothing$ as "null set" in the same way that I pronounce $<$ as "less than." Alternatively, I also read $A=\varnothing$ as "$A$ is null" as well as "$A$ is the null set." I also use empty, but others have mentioned that, and I thought I should add null as an alternative pronunciation. I would call the symbol itself either "null set symbol" much like I would call the symbol $<$ a "less than sign" or (less commonly) "less than symbol."
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