# Help:Questions

How Do I...
Please post site related problems on the main talk page.
i.e. Things not working as they should.

Just a note.

The delimiter $|$ doesn't seem to be valid in the eqn template, so I used \vert instead, but this behaves pretty weirdly, e.g.

 $$\displaystyle$$ $$\displaystyle$$ $$\displaystyle$$ $$\displaystyle$$ $$\le$$ $$\displaystyle$$ $$\displaystyle \left\vert { a_{m+1} } \right\vert + \left\vert { a_{m+2} } \right\vert + \cdots + \left\vert { a_n } \right\vert$$ $$\displaystyle$$ $$\displaystyle$$ Triangle Inequality

is fine, but

 $$\displaystyle$$ $$\displaystyle$$ $$\displaystyle$$ $$\displaystyle$$ $$\le$$ $$\displaystyle$$ $$\displaystyle \left\vert {a_{m+1} } \right\vert + \left\vert {a_{m+2} } \right\vert + \cdots + \left\vert {a_n} \right\vert$$ $$\displaystyle$$ $$\displaystyle$$ Triangle Inequality

is not.

Argh, also this:

 $$\displaystyle$$ $$\displaystyle$$ $$\displaystyle$$ $$\displaystyle \left\vert { \frac{a_n}{ n^s } } \right\vert$$ $$=$$ $$\displaystyle$$ $$\displaystyle \frac{ \left\vert { a_n } \right\vert }{ n^\sigma }$$ $$\displaystyle$$ $$\displaystyle$$ {{eqn|l= o=\leq r= \frac{ \left\vert { a_n } \right\vert }{ n^{\sigma_0} } {{eqn|l= o= = r= \left\vert { \frac{a_n}{ n^{s_0} } } \right\vert

can't make it work at all. Linus44

Placing two }'s side-by-side will prematurely close {{eqn}} template. This has been a topic of discussion on the main page ... we're still looking for a fix. --Joe (talk) 15:23, 15 February 2011 (CST)
Ok, thanks Linus44 15:30, 15 February 2011 (CST)
You missed some closing braces
 $$\displaystyle$$ $$\displaystyle$$ $$\displaystyle$$ $$\displaystyle \left\vert { \frac{a_n}{ n^s } } \right\vert$$ $$=$$ $$\displaystyle$$ $$\displaystyle \frac{ \left\vert { a_n } \right\vert }{ n^\sigma }$$ $$\displaystyle$$ $$\displaystyle$$ $$\displaystyle$$ $$\displaystyle$$ $$\displaystyle$$ $$\displaystyle$$ $$\leq$$ $$\displaystyle$$ $$\displaystyle \frac{ \left\vert { a_n } \right\vert }{ n^{\sigma_0} }$$ $$\displaystyle$$ $$\displaystyle$$ $$\displaystyle$$ $$\displaystyle$$ $$\displaystyle$$ $$\displaystyle$$ $$=$$ $$\displaystyle$$ $$\displaystyle \left\vert { \frac{a_n}{ n^{s_0} } } \right\vert$$ $$\displaystyle$$ $$\displaystyle$$

{{begin-eqn}}
{{eqn|l= \left\vert { \frac{a_n}{ n^s } } \right\vert
|o= =
|r= \frac{ \left\vert { a_n } \right\vert }{ n^\sigma }
}}
{{eqn|l=
|o=\leq
|r= \frac{ \left\vert { a_n } \right\vert }{ n^{\sigma_0} }
}} <------------------------------------------------------------------ here
{{eqn|l=
|o= =
|r= \left\vert { \frac{a_n}{ n^{s_0} } } \right\vert
}} <------------------------------------------------------------------ and here
{{end-eqn}}


--Joe (talk) 15:32, 15 February 2011 (CST)

I tried 4 times to add the same reply but I kept getting a midair collision. Stroll on. --prime mover 15:35, 15 February 2011 (CST)

## How do you post something on a discussion page?

How do you post something on a discussion page? --1is0? May 4, 2013

By pressing the link at the top of the page that says "Discussion". If it's blue, it means there's already such a page, to which you are welcome to add material. If it's red, then the page does not yet exist because nobody has posted anything to it yet. Your contribution will then be the first on that page. --prime mover (talk) 22:58, 4 May 2013 (UTC)

## Does the site have a standard quantifier convention?

For unbounded quantification, I've seen $$\forall x:\forall y:\exists a :(\dots)$$ when I would have written simply $$\forall x\forall y\exists a(\dots)$$

For bounded quantification, I've seen something similar (use of colons). However, I would simply write the quantification without the colons. --Robertbiggs34 (talk) 19:26, 27 May 2013 (UTC)

Also, when using bounded quantification and using the same quantifier over the same set (i.e. $$\forall x\in \R \,\forall y\in\R$$) do we shorten this to $$\forall x,y\in\R$$ or $$\forall x.y\in\R$$? --Robertbiggs34 (talk) 19:30, 27 May 2013 (UTC)

We use commas. I am not the style master here, so I can't answer the rest too well. I don't think colons should be needed between quantifiers, at least for unbounded quantification, but Prime.mover would be the one to answer definitively. --Dfeuer (talk) 19:33, 27 May 2013 (UTC)
$\forall x: \forall y: \exists a : \left({\ldots}\right)$ is the convention, consistent with colon meaning (loosely) "such that".
It's also $\forall x, y \in \R$ which is consistent with comma being used to separate entities in a list. I've never seen a dot used in this context, it looks perverse to me.
What we don't sanction is the use of a comma to mean "such that", so when we see $\forall x \in S, P \left({x}\right)$ we immediately change it to $\forall x \in S: P \left({x}\right)$, and so on.
Commas are probably the most ill-used punctuation mark in natural language as well as mathematics, so it's something we're used to.
Incidentally, please use dollar-sign delimiters instead of [itex] because the latter are not fully supported by MathJax (and dollars are more compact and quicker to type than the alternatives). --prime mover (talk) 19:42, 27 May 2013 (UTC)
Vector Space Axioms is a good illustration of PW style. --GFauxPas (talk) 20:12, 27 May 2013 (UTC)