Notation for the union of all the sets in a family.

Question

Does anyone know how to write the following: If $\mathcal{F}$ is a family of sets, I want the union of all $X$ in this $\mathcal{F}$.

Thanks in advance!

Just check this thread? http://math.stackexchange.com/questions/276104/online-mathjax-editor — Rivasa, Dec 12 '13 at 20:42
In some sense this is not a question about $\TeX$ or formatting, it's a question about the correct symbol and syntax to indicate the union of a family of sets. I don't see it so off-topic. Maybe it could be reworded... — rewritten, Dec 12 '13 at 22:06
If the question is reworded so that it asks for the current notation for union of family of sets, then I say reopen it. But if it specifically is about one can typeset something in LaTeX, then I say migrate it. Maybe the OP could scan a picture of what he is trying to do in LaTeX, then the Tex-people would know what the best way to do that is. — Thomas, Dec 12 '13 at 22:31
This looks like more of a math notation question than a $\TeX$ question. The Help Center is unclear about whether such a question belongs here. — Stefan Smith, Dec 13 '13 at 01:01
On second thought, the fact that a (notation) flag even exists suggests that the question does belong here. This a notation question. — Stefan Smith, Dec 13 '13 at 02:21
IF the OP could agree to the changing of his question, then I am also fine with how it stands now. However, the original question asked specifically about how to do something in LaTeX. — Thomas, Dec 13 '13 at 02:29

score 1 · Answer 1 · edited Aug 18 '16 at 21:05

1

Use $\bigcup_{X \in \mathcal F} X$ or simply $\bigcup \mathcal F$.

edited Aug 18 '16 at 21:05

Alex Ortiz

answered Dec 12 '13 at 20:43

Hagen von Eitzen

In code this would be $\bigcup_{x\in\mathcal{F}}X$ or $\bigcup\mathcal{F}$ . – egreg Dec 12 '13 at 20:53

score 1 · Answer 2 · answered Dec 12 '13 at 20:43

1

This probably should be migrated to tex.SE.

But:

$$ \bigcup_{X\in \mathcal{F}} X $$ would work.

answered Dec 12 '13 at 20:43

Thomas

1

But would the typographers there know about the math background of th equestion? – Hagen von Eitzen Dec 12 '13 at 20:44
@HagenvonEitzen: Maybe you are right. I would guess that they would. – Thomas Dec 12 '13 at 20:44

score 0 · Answer 3 · answered Dec 12 '13 at 20:42

0

Use $\bigcup_i X_i$, if $\mathcal F=\{X_1,X_2,\dots\}$.

answered Dec 12 '13 at 20:42

Avitus

3

How do you know that $\mathcal{F}$ is countable? – Thomas Dec 12 '13 at 20:43
I did not know it: I thought that the OP needed the union symbol, after all...instead of counting the "i"'s one can write $X\in\mathcal F$ under the union. – Avitus Dec 12 '13 at 20:45

3 Answers3