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Nov 21, 2007, 6:34:43 AM11/21/07

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Hello,

as far as I know the "official" symbol for union disjoint (between two

sets) is the \cup symbol with a dot placed in the middle. To use it,

you can define the new command \dotcup

\newcommand{\dotcup}{\ensuremath{\mathaccent\cdot\cup}}.

But what operation is symbolized by the \oplus symbol?

Kind regards,

Sascha

Nov 21, 2007, 6:43:16 AM11/21/07

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On Wed, 21 Nov 2007 03:34:43 -0800 (PST), piramido wrote:

> But what operation is symbolized by the \oplus symbol?

> But what operation is symbolized by the \oplus symbol?

Nov 21, 2007, 6:55:30 AM11/21/07

to

Yes, that's right. Thank you. But what I really wanted to know is what

the symbol \uplus stands for.

Kind regards,

Sascha

Nov 21, 2007, 6:45:01 AM11/21/07

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piramido schreef:

This is not really a TeX question. You’d be better off in one of the

newsgroup with ‘symbol’ or ‘typography’ in their name.

Anyway, it is often used for exclusive or in the logic literature, or as

a dual operation for normal addition if the context requires it, or …

See http://www.unicode.org/charts/PDF/U2200.pdf, symbol 2295.

H.

--

Hendrik Maryns

http://tcl.sfs.uni-tuebingen.de/~hendrik/

==================

http://aouw.org

Ask smart questions, get good answers:

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Nov 21, 2007, 7:42:52 AM11/21/07

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Thank you.

On 21 Nov., 12:45, Hendrik Maryns <gtw37b...@sneakemail.com> wrote:

> Anyway, it is often used for exclusive or in the logic literature, or as

> a dual operation for normal addition if the context requires it, or ...

.. but it is not used for the disjoint union, right?

Kind regards,

Sascha

Nov 21, 2007, 7:27:23 AM11/21/07

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piramido schreef:

Whatever you want it to stand for. In mathematics, it is common

practice to introduce a symbol for some operations one needs in some

context. This can be anything. Only if an operation gets very common,

sometimes the notation solidifies, and one can talk about ‘the’ symbol

for it. But some symbols are just symbols that happen to sort of

express what one wants to use them for.

See the same link I sent you above, symbol \U228E, it is called

‘Multiset union’ there.

But why do you want to know? Just use the symbol as it suits your needs.

Nov 21, 2007, 7:51:09 AM11/21/07

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On Wed, 21 Nov 2007 03:55:30 -0800 (PST), piramido wrote:

> On 21 Nov., 12:43, Bob Tennent <B...@cs.queensu.ca> wrote:

>> On Wed, 21 Nov 2007 03:34:43 -0800 (PST), piramido wrote:

> On 21 Nov., 12:43, Bob Tennent <B...@cs.queensu.ca> wrote:

>> On Wed, 21 Nov 2007 03:34:43 -0800 (PST), piramido wrote:

>> > as far as I know the "official" symbol for union disjoint

>> > (between two sets) is the \cup symbol with a dot placed in the middle.

>> > (between two sets) is the \cup symbol with a dot placed in the middle.

>> > But what operation is symbolized by the \oplus symbol?

>>

>> http://en.wikipedia.org/wiki/Direct_sum

>

> Yes, that's right. Thank you. But what I really wanted to know is what

> the symbol \uplus stands for.

>>

>> http://en.wikipedia.org/wiki/Direct_sum

>

> Yes, that's right. Thank you. But what I really wanted to know is what

> the symbol \uplus stands for.

There is no "official" symbol for disjoint union (indeed, no "official"

symbol for anything). If you google for disjoint union, you'll see +,

|, oplus, upside-down pi, uplus, oplus, and even dotted cup, as you've

suggested, all used.

Bob T.

Nov 21, 2007, 10:07:29 AM11/21/07

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piramido schreef:

You still don’t get it, do you? There is no official symbol for

anything. What would ‘official’ mean here?

Well, there is ISO, of course. You might want to have a look at ISO

31-11:1992 [1], but I do not know whether disjoint product is in there,

I didn’t buy it. Ah, there is a Wikipedia article, of course, which

doesn’t mention disjoint union: http://en.wikipedia.org/wiki/ISO_31-11

I also urge you to read the page referenced from there, so that you know

what you are talking about:

http://en.wikipedia.org/wiki/Mathematical_notation.

H.

[1]

http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=3653

Nov 21, 2007, 7:40:13 AM11/21/07

to

piramido <pira...@googlemail.com> writes:

> Hello,

>

> as far as I know the "official" symbol for union disjoint (between two

> sets) is the \cup symbol with a dot placed in the middle.

(sorry for this OT posting)

Well, I think that depends on the discipline. I have seen this

"dotcup" used in analysis, but in my field of geometry/topology I have

only seen \sqcup used (if a special symbol is used at all, and not

just \cup with an explanation in words that the sets are disjoint).

Also, there is sometimes a semantic difference as to what is meant by

"disjoint union" of two sets. Sometimes one means simply the union of

two sets which happen to be disjoint, while in other circumstances one

_declares_ two sets to be disjoint (formally by some standard

set-theoretical construction) and then take their union. For instance

$R \sqcup R$ might be used to denote a topological space consisting of

two disjoint copies of the real line. I don't know if \dotcup and/or

\sqcup are more often used in one context or another.

--

Rasmus Villemoes

<http://home.imf.au.dk/burner/>

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