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When using the amsthm package with the \eqref command, things may not be correct. When the main font of a theorem is italic, the \eqref is non-italic while \ref is italic. Please, see the provided code. Is all this consistent?

\documentclass[12pt,fleqn]{book}
\usepackage{amsmath,amsthm}
\newtheorem{theorem}{Theorem}
\begin{document}
\begin{equation}\label{eq:1}
\cos \pi=-1
\end{equation}
\begin{theorem} In Equation~(\ref{eq:1}) or in Equation~\eqref{eq:1}...
\end{theorem}
\end{document}
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2  
Yes, \eqref is designed just to give roman type also in italic context. –  egreg Apr 7 '11 at 23:09
    
but it should not, should it? –  pluton Apr 7 '11 at 23:51
1  
equation tags are normally typeset in roman type, so it can be considered correct to reference them in the same font type. –  Gonzalo Medina Apr 7 '11 at 23:59
2  
according to accepted style (observed by other publishers as well as ams), all punctuation and digits in the statements of theorems should be upright. these days, this is ignored more often than it is observed, but if you look at a well-produced math publication from the days when it was typeset in metal, you will find this to be true. it probably grew out of a desire to avoid clashing shapes of parentheses and the like between math (where they are always upright) and the surrounding text, even if that is italic. –  barbara beeton Apr 8 '11 at 12:46
    
@pluton: Despite this, it may be a user preference to have a different style for referencing (conforming to the surrounding font shape). However, this may also be very subjective; as in, I like it, but nobody else does. In that case, \renewcommand{\eqref}[1]{(\ref{#1})} puts you back to square one... –  Werner Aug 6 '11 at 17:03

1 Answer 1

up vote 5 down vote accepted

There is what I think is a very good explanation of this is the mathtools manual in paragraph 3.2.2, where they discuss the \refeq command introduced by mathtools. They explain that \refeq, just like \eqref, uses upright font even in the middle of italics text to "avoid what could possibly lead to confusion in cases where the tag font has very different form in upright and italic shape".

They give an example where they use "Q&A" as a tag while the font is set to Palatino. Apparently in Palatino, the character & looks very different in italics than in upright, so the reference in italics would look very different from the actual tag, which is upright.

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