What is the convention around appositional phrases and commas in formal mathematical writing?

Question

Does anyone have any useful guidelines for comma usage around appositional phrases in article writing? For instance which are preferred among the following pairs?

1. A group $G$ is nilpotent if...
2. A group, $G$, is nilpotent if...

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3. The Klein-4 group $K_4$ is...
4. The Klein-4 group, $K_4$, is...

I believe that 1 and 3 are preferred, but in the second example this conflicts with the way we use commas when not writing mathematics, e.g., "The first man on the moon, Neil Armstrong,..." we use commas because the first phrase uniquely identifies Neil Armstrong, and so adding his name is not essential to the meaning of the sentence.

I'm particularly worried about the following thing I've written:

"The jump, $Y'$, of $Y$..."

Here I think the commas are needed (as I'm interrupting a phrase). I wrote it this way because I didn't want to write "The jump of $Y$ $Y'$" which looks like nonsense.

Answer 1

You are right, models 1. and 3. are preferred in mathematics; in your last example, I would avoid the comma too (adding a "that is" or "i.e.").
In general, follow this rule: "make it simple" when writing mathematics or computer science texts.