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A question for English speakers. When using (or reading) the symbol $\setminus$ to denote set difference —

$$A\setminus B=\{x\in A|x\notin B\}$$

— how do you pronounce it?

If you please, indicate in a comment on your answer what region you're from (what dialect you have).

This is a poll question. Please do not repeat answers! Rather, upvote an answer if you pronounce the symbol the same way the answerer does, and downvote it not at all. Please don't upvote answers for other reasons. Thanks!

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How do you pronounce it? – lhf Feb 28 '12 at 17:57
This should perhaps be CW. – user21436 Feb 28 '12 at 18:08
@KannappanSampath: I already flagged this for a moderator. – Asaf Karagila Feb 28 '12 at 18:09
I say CW also. People upvote to pick which one they agree with. – Graphth Feb 28 '12 at 20:21
I pronounce it "$\setminus$" of course. How else would I pronounce it? – Zarrax Feb 28 '12 at 22:22

10 Answers 10

I usually say "A without B," but it depends on my mood that day

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I'm from Ontario, did my undergrad at Waterloo – you Feb 28 '12 at 17:56
(Comment from upvoter.) I'm American. – msh210 Feb 28 '12 at 18:02
If someone said this out loud, without a visual cue, I would have no idea what it means. – Carl Mummert Feb 28 '12 at 18:09
@Carl even within the context of (mathematical) sets? Spoken language is always context sensitive and once you have the context I find this entirely understandable and natural. – Konrad Rudolph Feb 28 '12 at 20:04
@Konrad Rudolph: yes, even in the context of mathematics I would not recognize "without" to refer to a relative complement unless someone explicitly told me that it did. – Carl Mummert Feb 28 '12 at 20:41

$A$ minus $B$ seems to be the natural way.

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I'm not a native English speaker. – lhf Feb 28 '12 at 18:00
This is how I say it, and I am a native speaker. This is also why the symbol is named "setminus". – Carl Mummert Feb 28 '12 at 18:09
As an English speaking programmer (not mathematician) that's how I'd say this – Ben Brocka Feb 28 '12 at 19:58

Complement of B in A for A-B or sometime A difference B

This is more self explaining way to say.. I feel!

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This is what seems to me the right way! – user21436 Feb 28 '12 at 18:07

No one's mentioned "$A$ take away $B$" yet.

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But is that the way you in practice pronounce it? – Mitch Feb 28 '12 at 18:24
@Mitch Usually, yes. Especially when the sets in question are collections of generic objects, such as people, chairs, etc... – David Mitra Feb 28 '12 at 18:34
That doesn't sound very mathematical. +1 – JMCF125 Jun 14 '13 at 16:15

I say "A slash B".${}{}{}{}{}{}{}{}$

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I guess there's not too much confusion between this and $A/B$, A modulo B :P – you Feb 28 '12 at 19:33

I pronounce $A \setminus B$ just as the latex code: $A$ setminus $B$.

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Reading letters with their latex command names usually puts me off... To hear someone seriously saying varepsilon makes me distrust him! – Mariano Suárez-Alvarez Feb 28 '12 at 23:50
I should perhaps stop writing this as "A \backslash B"... – Tanner Swett Feb 28 '12 at 23:59

A less B.............................

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This is what I was taught (in Ireland). – TRiG Feb 28 '12 at 20:28

I say any of the following (it varies):

"A not B"

"A slash B"

and when I am trying to be clear

"The complement of B in A"

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Prologue: I usually try NOT to pronounce math symbols or expressions or say it loud in mind as (claimed in folklore) that internal reading seems to hinder 'speed reading' or comprehension. (Note: I am hugely influenced by Eastern arts so may be there is some truth to that. (Meta-note: Feel free to comment on it if you disagree))

Vote status: Upvoted for making me look up some links.


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In situations such as the theory of automorphic forms/functions, the expression $A\backslash B$ means "$B$ left mod $A$", not set-complement. It is pronounced that way: "B left-mod A".

This is necessary because there are quotients on the right also, which interact with these. It amazes me how much trouble it is to get students to "recover from" thinking that "backslash" could only mean "set complement". I say to them "why not just write '-' for set complement?".

The literature on automorphic what's-its is full of left quotients, notated $A\backslash B$.

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