# Is it possible to declare document to be math-free to stop “Missing $inserted”? I know that it it possible to either escape every single underscore (\_), or apply \usepackage{underscore}. Escaping is tedious, underscore package breaks \textbf{a_b} and \includegraphics{filename_with_underscore}. Is there a better solution for math-free texts including multiple underscores (in my case - in URLs)? • If you use hyperref, you can go with \url{http://www.example.com}, the url package offers a similar command. – moewe Dec 22 '14 at 10:21 • _ should work without problens in includegraphics – David Carlisle Dec 22 '14 at 10:25 • Welcome to TeX.SX! If the document is math free, then \catcode_=12 in the preamble will do, provided you also have \usepackage[T1]{fontenc} – egreg Dec 22 '14 at 10:26 • it is better to mark URL with \url{http://.....} (url or hyperref) as then line breaking is better handled but if you want _ to be a normal character use \catcode\_=12 make sure you have \usepackage[T1]{fontenc} as OT1 fonts do not have the _ character. – David Carlisle Dec 22 '14 at 10:27 • hyperref adds hyperlinks to URLs (these are by default marked with boxes), you can disable this behaviour or modify it (see, here for example), line breaking in URLs is a tricky issue (see for example here) – moewe Dec 22 '14 at 11:25 ## 2 Answers It is better to mark URL with \url{http://.....} (url or hyperref) as then line breaking is better handled. Note that url package will just allow linebreaking in URLs and doesn't add any annotation. hyperref uses the same code for linebreaking but also makes the link an active link. By default this adds coloured decoration but the package has several options to control or disable that. But if you want _ to be a normal character use \catcode\_=12  make sure you have \usepackage[T1]{fontenc}  as OT1 fonts do not have the _ character. You can have your underscores print as such outside math mode and doing their usual business in math mode: \documentclass{article} \usepackage[T1]{fontenc} \catcode_=12 \begingroup\lccode~=_\lowercase{\endgroup\let~\sb} \begin{document} Under_score and$a_{1}$. \end{document}  For the problem of colored URLs, just load hyperref with the relevant option. With \urlstyle you can also change the default font. \documentclass{article} \usepackage[T1]{fontenc} \usepackage{hyperref} \hypersetup{colorlinks=false} \catcode_=12 \begingroup\lccode~=_\lowercase{\endgroup\let~\sb} \begin{document} Under_score and$a_{1}\$, see at
\url{http://tex.stackexchange.com}

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\urlstyle{rm}

This URL uses the normal font
\url{http://tex.stackexchange.com}

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• It seems that Knuth has prepared the \mathcode of _ as math-active (which starts to be active if the catcode of _ is changed from 8 to 12), but this activity has had another purpose: to draw the underline character. Maybe the reason was that Knuth has had missing underline character in his fonts. This is very curious historical reason why we have not set the _ as math-active to do \sb and \catcode_=12 by default in all formats. Unfortunately. – wipet Dec 23 '14 at 6:10
• @wipet The fact that the glyph _ is not in cmr10 has certainly to do with this. Anyway, I stand with the choice of making _ category code 8, as it helps in catching syntax errors. – egreg Dec 23 '14 at 9:28