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I've always known that $\emptyset$ is called an empty set or null, until recently, when I heard someone calling it zed. I looked it everywhere but couldn't find this naming.

Is "zed" a valid name for the $\emptyset$ symbol?

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Zed's dead baby, Zed's dead. – Asaf Karagila Feb 26 '14 at 20:45
@AsafKaragila Best comment I've read in months. – Brian Fitzpatrick Feb 26 '14 at 20:45
No. It's not a valid name for the empty set. – Potato Feb 26 '14 at 21:08
Zod. All kneel before the power of Zod: $\{\varnothing\}$. – Pedro Tamaroff Feb 28 '14 at 10:30
up vote 2 down vote accepted

Personally, I have never heard it called that (of course, it is always possible that some in subfield of mathematics I'm not familiar with, it is an accepted name). However, non-Americans will usually call $\mathbb{Z}$ (the integers) "zed", perhaps you misunderstood?

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Misunderstood? No. But I strongly believe that the person doesn't know the actual meaning of $\emptyset$. – slybloty Feb 26 '14 at 20:54
Then I think it'd probably be best to just ignore what they call it :) – Zev Chonoles Feb 26 '14 at 20:56
"First of all - it's YY-Zed". :) – Asaf Karagila Feb 26 '14 at 21:11
@rschwieb: I actually find that quite surprising. You don't say ahr ehn for the expression $\mathbb{R}^n$, or cee adjoin x for $\mathbb{C}[x]$? – Zev Chonoles Feb 26 '14 at 21:33
@rschwieb: Still, I think > 90% of the time I would say let x be in zee, and this is true of any of my professors and peers I can remember. – Zev Chonoles Feb 26 '14 at 21:42

First of all, there are two similar symbols:

U+00D8 Ø latin capital letter o with stroke

U+2205 ∅ empty set

The first is a letter used in Danish, Norwegian, and Faroese languages. The second is the empty set symbol. The rendering of "\emptyset" on this site looks like the first, and ought to look like the second, in my opinion.

Now, after that diversion, back to your question ... English people use "zed" to refer to the last letter of the alphabet (the thing that Americans call "zee") regardless of whether they are talking about the set of integers or not.

I have lived in both England and the US for decades, and never heard anyone use "zed" to refer to the empty set in either country.

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