math-modepunctuationspacing
I need write some formula, but I don't know how to arrange the comma's place.
$p,\ q\in N$, blabla $0<a,\ b<1$ blabla $i,\ j=1,\ 2,\ \dots,\ n$
or
$p,\;q\in N$, blabla $0<a,\;b<1$ blabla $i,\;j=1,\;2,\;\dots,\;n$
or
$p$, $q\in N$, blabla $0<a$, $b<1$ blabla $i$, $j=1$, 2$, $\dots$, $n$
or
$p$,~q\in N$, blabla $0<a$,~$b<1$ blabla $i$,~$j=1$,~$2$,~$\dots$,~$n$
which one is more acceptable?
You don't need TikZ for this. If you're using LaTeX, you just need amsmath and the mathtools package (both of which you likely have):
\documentclass{minimal}
\usepackage{amsmath}
\usepackage{mathtools}
\begin{document}
\[\begin{matrix}
x \xleftarrow{\quad R\quad} \mathcal{Z}_q &\quad
\xrightleftharpoons[\beta=g^y]{\quad\alpha=g^x\quad} \quad&
y \xleftarrow{\quad R\quad} \mathcal{Z}_q \\
g^{xy} & & g^{xy} \\
\end{matrix}\]
\end{document}
This produces the following output:
The amsmath package provides the \xleftarrow and \xrigharrow commands, which set an eXtensible \leftarrow and \righarrow, respectively; their mandatory argument is set on top, and their optional argument is set below (\xleftarrow[below]{above}). Normally, it's just as wide as necessary for the text, so I inserted \quads around the text to space it out. The mathtools package, which extends amsmath, provides more extensible arrows, including \xleftrightarrow (for an extensible ↔), \xLeftrightarrow (for an extensible ⇔), \xleftrighharpoons (for an extensible ⇋; the upside-down version of the symbol in the example picture), and \xrightleftharpoons (for an extensible ⇌, as seen in the example picture), any of which could be used here depending on your tastes.
Also, note that you shouldn't need to space out the \xrightleftharpoons like I did (which is why there's &\quad ... \quad&), but apparently I needed to here (though in LaTeXit I didn't, so with some small change you probably wouldn't need to). You only need the matrix here since you want to align the g^{xy}s with the first and third arrows; if you just wanted the top line, you wouldn't need to bother.
I think it's just personal preference. In the standard setup * and \ast are the same.
fontmath.ltx has
\DeclareMathSymbol{*}{\mathbin}{symbols}{"03} % \ast
\DeclareMathSymbol{\ast}{\mathbin}{symbols}{"03}
So both pick up character 3 from the symbol font with infix binary operator spacing.
Best Answer
There are some subtleties in this kind of sentences.
You have to decide whether the space in something like "p and q belong to N" you want a normal space after the comma or not and then be coherent across the document. So you can do either
or
In the first form the tie is necessary, or you may get
which is unacceptable. I prefer, for this case, the second form that makes clearer that the two variables are treated in the same fashion. In this case we can consider that the comma belongs to the formula, being just a shorthand:
$p,q\in N$actually stands for the longer and clumsy$p\in N$ and $q\in N$.To the contrary, some conditions applying to one or more variables should better go in different formulas; therefore
should be considered wrong because (as shown in the comments below, which refer to the previous version of this answer) it is ambiguous: does it mean that a is greater than zero and b is less than one or that both should be between zero and one? So separate them:
should be preferred if both variables vary between zero and one. One might use
which seems, however, a bit too technical.
Something similar applies to ranges, but the commas in the range aren't part of the formula, so
is, in my opinion, the preferred way to go. For the first bit the choice made for the above case should be respected, of course. One might also do
so as to ensure that no line break is taken after the 1. In difficult line breaking cases, that tie can be removed. There's no problem with a line break after the dots, because a range is expected. An input such as
results in too crowded an output (and poses line breaking problems).
A hint: whenever you feel the necessity to use
\␣(control space) or\;in a formula, ask yourself whether it's better to do separate formulas.