# Punctuation in equations

My document will contain a lot of equations, and as usual in that case I would like to use "punctuation" in the equations, like commas, colons, periods/full stops, semicolons, etc.

Is there a special way to correctly do that? Now I just type these characters at the end of the equations, but as it's in math mode maybe there is a better way that improve the spacing, etc.

I also read about \colon, \ldotp. What do they do that the normal "characters" don't?

• \colon changes the spacing for use in defining a function: f \colon A \to B, it would look funny if used as a colon serving its normal text purpose. Feb 23, 2011 at 12:16

## 1 Answer

No, you can key in the punctuations marks as usual. As Seamus writes in his comment, macros like \colon are for punctuation marks that are being used as mathematical relations rather than punctuation.

Sentence punctuation should not appear inside of inline mathematics. For displayed mathematics, I think it's safe to say it's a matter of style. See "For formal articles, should a displayed equation be followed by a punctuation to conform to the language grammar?" I'm in the camp of no sentence punctuation in display math; it's just distracting. De gustibus non est disputandum.

So for example:

If $a$ and $b$ are the lengths of the legs of a right triangle
and $c$ is the length of the hypotenuse, then $a^2 + b^2 = c^2$, or:
$c = \sqrt{a^2 + b^2}$
This amazing relation is known as the \textbf{Pythagorean Theorem}.

• I agree it is a matter of style, but I'm a bit more on the other side :p Anyway I just have to use normal punctuation marks in that case. Is there something special to do with the spacing ? Like \,; to force a larger spacing ? Feb 23, 2011 at 13:14
• @Cedric H.: If you wouldn't put spacing after a word before a semicolon, why would you put it after an equation? Just my opinion. Feb 23, 2011 at 13:16
• @Matthew Leingang: Good point :p Feb 23, 2011 at 13:33
• @Mathew Leingang: in some land (Switzerland for example) you must put a thinspace before a semicolon. So the question stays.
– PHL
Feb 23, 2011 at 16:50
• @Matsaya: Interesting. Then let me broaden to say I think it should be the same with (inline) equations as it is with natural language sentences. Feb 23, 2011 at 18:27