# “$a, b$” vs. “$a$, $b$”

I have two questions.

1. Would you use Let $x, y$ and $z$ be real numbers. or Let $x$, $y$ and $z$ be real numbers. ? Which one is better?

2. Would you use For $x, y\in\mathbb R$ we have ... or For $x$, $y\in\mathbb R$ we have ... ? Which one is better?

• I would use $x$, $y$, and $z$ and $x, y \in \R$. – Manuel Apr 21 '16 at 14:35
• I edited to use inline code, which is easyer to read in your case, but as a general comment, for your text to appear as code when you insert 4 spaces before, it also needs to be preceeded by an empty line. – Samuel Albert Apr 21 '16 at 14:35
• I say 2nd choice: $x$, $y$ and $z$, sine it is Englishy text. I use the first choice for $f(x,y)$. – Steven B. Segletes Apr 21 '16 at 14:35
• – Ulrike Fischer Apr 21 '16 at 14:48
• Regarding the first question: The second option is the correct one. In the sentence "Let x, y and z be real numbers," x, y and z fulfill the same syntactic roles as Tom, Dick and Harry do in the sentence "Let Tom, Dick and Harry be adult males." The fact that x, y and z are mathematical formulas and are entered using $symbols is secondary. In consequence, the commas should not be included in the math-mode material. – Mico Apr 21 '16 at 14:48 ## 1 Answer I think you have asked several questions. The first is about$x, y$versus$x$,$y$. I think the second one is semantically and hence typographically right since the comma is not part of the mathematical expression. Your second example is a little ambiguous. There I would include the comma in the mathematics. An implicit question is the choice between Let$x$and$y$be real numbers and Let$x, y \in \mathbb{R}\$

That's a question of style. I find words easier to read than symbols, but your taste may differ.

• not 100% sure... will delete the comment. Thanks! – Rmano Apr 21 '16 at 20:06