# Comma semantics

I am wondering about whether to use text or math comma in the following cases (because they carry different spacing), and whether if style guides actually have comments on these.

• The points A, B and C are on the same line.

• $a, b \in S$ or $a$, $b \in S$

• $i = 1, 2, \dots, n$ or $i = 1$, $2$, $\dotsc$, $n$

Comparison for the last one:

$i = 1, 2, \dots, n$

$i = 1, 2, \dotsc, n$

• I'm sure this has been answered before, but I'm not sure what to search for. This should be entered as appropriate for the meaning. In both cases, the entire expression is a single math unit, and should be in a single pair of \$. Not long ago, there was a question that asked what to do if such an expression came at the end of a line, and it really had to be split; that would shed some additional light on this, but (as I said), I'm not sure how to search for that. By the way, you really don't want \dotsc; the dots should be on the line. – barbara beeton May 21 '20 at 3:53
• \dotsc specifically means dots between commas. I actually used cdots everywhere before, then realized ldots is the convention. – Max Xiong May 21 '20 at 5:06
• Urk. You're correct; \dotsc is indeed "dots with commas. (Confusing with \cdots.) Thanks for correction. – barbara beeton May 21 '20 at 5:12