# Vertical position of punctuation following fractions in display-style equations

Assuming that one wants punctuation in equations, what is the best way to adjusting the vertical position of the punctuation if it follows a fraction? I am using Palatino and Euler here (which I generally really like). The problem is especially apparent with commas, which end up looking like primes on elements in the denominator (without a prime close by, the first equation looks an awful lot like it has a B' in the denominator): Adding some space before the punctuation (second example) helps slightly, but still looks strange to me. It seems that, when following a fraction, the comma (and maybe the period) should be raised by a small amount (third example).

## Questions

1. What is the best typographic practice for including punctuation in these cases?
2. Is there a robust way of doing this? I.e. one that somehow uses font information to work well in all sizes and fonts.

Obviously raising of punctuation should only occur in specific cases such as the fractions shown here. Perhaps there is a way of inserting something at the end of fractions that will trigger this behaviour, then reset it if the following text is not punctuation?

Here is the MWE I used to make the output above:

\documentclass{minimal}
\usepackage{mathpazo}                      % To get Palatino
\usepackage[small, euler-digits]{eulervm}  % and now Euler

\begin{document}
Here are two equations that look awfully similar:
\begin{equation}
a = \frac{1}{A+B}, \qquad b = \frac{1}{A+B'}.
\end{equation}
\begin{equation}
a = \frac{1}{A+B}\,, \qquad b = \frac{1}{A+B'}\,.
\end{equation}

\newcommand\raisepunct{\,\mathpunct{\raisebox{0.5ex}{#1}}}
\begin{equation}
a = \frac{1}{A+B}\raisepunct{,}
\end{equation}
\end{document}


## Related Questions

Several questions have addressed punctuation in equations, but most discuss only whether or not to include it, or if a thin horizontal space should be included:

• Related Question: comma like \cdot which shows how to adjust the position of the comma. Mar 31, 2012 at 2:23
• As for your second question: it shouldn't be difficult to redefine \frac (and \dfrac) to look ahead and if the next token is a comma, then gobble it and put one itself, raised a bit. But man, this is a good question. I'd upvote it twice if that were possible... Mar 31, 2012 at 2:33
• @PeterGrill Thanks: I missed that one (I will add it to my list of related questions.): \mathpunct could be used but still requires tweaking (though 0.22em should be 0.5ex as in your solution... doh). Do you know if there is a way of increasing the default spacing provided by \mathpunct? @mbork I suspect you are right, but I worry about if there are any situations where this might cause problems (or incompatibility issues). I should probably look through the ams classes. Mar 31, 2012 at 3:26
• @mforbes The third option indeed looks better, but if, for whatever reason, anyone needs a letter after the comma, it will look most ugly. Try putting it inline, for instance… So, you might need to limit the modification to environments such as equation. Perhaps a raised variant to Will Robertson's answer could be a semantic solution to your problem. Mar 31, 2012 at 6:56
• I endorse proper punctuation in math displays (I usually put commas at the end of cases lines, for example), but not at all costs: if the punctuation can lead to ambiguity, some remedy has to be taken. Raising the sign is out of the question, I'd probably look for a way to avoid it or I'd put an additional thick space. Mar 31, 2012 at 9:28

The typography as displayed by LaTeX is the correct one. A comma needs to be placed at the baseline.

If you need to make any adjustments rather place the fraction within brackets. Agreed that the comma can be mistaken as a prime, but remember that mathematics is read in context, i.e., if no primes are used on the variables it is highly unlikely that a mathematically inclined reader will mix it up.

I have checked the above with a couple of books and always the comma is as shown by LaTeX. \documentclass{article}
\usepackage{amsmath}
\usepackage{mathpazo}                      % To get Palatino
If the number of independent variable is~$n$, we must have
$p = - \frac{n-2}{2}, \quad \text{or} \quad -\left(\frac{n-2}{2} + 1\right), \quad -\left(\frac{n-2}{2} + 2\right),\quad \left(\frac{n-2}{2+a}\right), \quad \dots.$

Your suggestion of raising the comma can lead to other problems such as \$(a,b)\frac{a}{b}, resulting in the commas not lining up.
• Good point about using parentheses to avoid confusion. As for context helping: probably not enough given that I was made aware of this issue by a confused, but mathematically inclined, colleague. I am still not convinced though: I think that shifting all punctuation up a bit looks better (at least with the Palatino comma). Maybe I should use the Euler comma in equations? There is no confusing that with a prime! \DeclareMathSymbol{,}{\mathpunct}{letters}{59} Apr 2, 2012 at 4:40