Another suggestion is you can also type: Alt + 0216.
Best regards,
Dan
Hi! I'm Dan! An Independent Advisor and also a Microsoft user for several years. I'll be more than happy to assist you today!
Method 1:
The ∅ symbol can be entered by going into "Symbols", choose "Mathematical Characters" and from the dropdown "Subset".
Method 2:
Type 2205 and then press "Alt + X".
I hope this information is helpful. Please keep me updated on the status of this issue. If you have any more questions, feel free to ask and I will be glad to assist you.
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Best regards,
Dan
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This is sufficiently rare, and handled in sufficiently many different ways, that you should always state explicitly how you're treating it. In my experience, the most common symbols are:
, 
, 
or similar on the more computer-sciencey side, and
or 
on the more logicy side.- Note that "
" is also used to denote contradiction, and "
" is also used as a predicate to denote "is undefined" or "doesn't halt" with "
" denoting "is defined"/"does halt."
- Note that "
But again, I'd explicitly state which you're using - although admittedly multiple of these would almost certainly make it obvious from context.
You can use some kind of Many-valued logic, but you said you want to put it simply. In SQL there is 3-valued logic with "null"/"unknown", for example.
According to Wikipedia André Weil (and maybe others) introduced the symbol $\emptyset$ for the empty set. They were inspired by the letter Ø in the Norwegian and Danish alphabet. So, I guess you could argue that the symbol should be pronounced as it is pronounced in these alphabets.
In my experience most mathematicians just call the symbol "empty set".
Note also, that the Wikipedia article says that the symbol is not to be confused with the Greek letter $\phi$ or $\Phi$.
Although not mathematics, I thought I would add that in the APL programming language the empty vector is represented by the symbol ⍬, which is pronounced "zilde".
So in math, I've always been taught to write my zeros with a small slash through them to differentiate between them and the letter O. Also, there's the symbol "∅" which denotes the empty set and is called the 'null sign'. If you are doing math in Norwegian or Danish, how do you avoid confusing the letter ∅ with these symbols?