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Using the class amsart, with

\usepackage[theoremfont]{newtxtext}  

the command \textbf has no effect in the the body of a theorem.

I am using TeXlive 2020, on MacOS.

Any solutions, explanations? Changing the order in the preamble doesn't solve the problem.

newpxtext doesn't have this problem. MWE:

\documentclass{amsart}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}

\usepackage[theoremfont]{newtxtext}

\theoremstyle{plain}
\newtheorem{theorem}{Theorem}

\begin{document}
\begin{theorem}
    Normal text. \textbf{Bold text.}
\end{theorem}
\end{document}

1 Answer 1

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The theoremfont option changes the font used in the plain theorem style (as defined by amsthm) to a special version of the italic font that has upright digits, parentheses and punctuation.

The (devious) trick it uses is to assign this special font to the slanted shape and in the font definition file t1ntxtlf.fd we find

\DeclareFontShape{T1}{ntxtlf}{m}{sl}{<-> \ntx@scaled ntx-Italic-tlf-th-t1}{}
\DeclareFontShape{T1}{ntxtlf}{b}{sl}{<->ssub * ntxtlf/m/sl}{}
\DeclareFontShape{T1}{ntxtlf}{bx}{sl}{<->ssub * ntxtlf/m/sl}{}

so there is no bold version for this font.

Workaround: use \textbf{\textit{Bold font.}}

\documentclass{amsart}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}

\usepackage[theoremfont]{newtxtext}

\theoremstyle{plain}
\newtheorem{theorem}{Theorem}

\begin{document}

\begin{theorem}
Normal text. \textbf{\textit{Bold text.}}
\end{theorem}

\end{document}

enter image description here

Or simply don't use boldface in theorem statements, which is much better.

4
  • Thanks for the prompt and expert answer! I don't usually use boldface in theorem statements. I was correcting someonelse's TeX file, and decided to replace his fonts with newtx. He was using $\mathbf{x}$ which gives an upright bold "x" in the theorem text. newtxtext "destroyed" this effect! Anyway: the author of newtx should warn about this, in his (very long) documentation.
    – rlsx
    Commented Apr 18, 2021 at 22:28
  • 1
    @rlsx As far as I can see, $\mathbf{x}$ works as expected. Not \textbf, though, as you discovered.
    – egreg
    Commented Apr 18, 2021 at 22:32
  • Another problem with "newtxtext" : it won't keep footnote numbers straight in an italic context (whether "theorem" or inside \emph{...} )
    – rlsx
    Commented Apr 18, 2021 at 23:31
  • $\mathbf{x}$ works indeed as expected. I was mistaken. What actually happens: if you load package biolinum after newtxtext but before newtxtmath, it kills the boldface in $\mathbf{x}$, apparenly everywhere. Independently of the option theoremfont.
    – rlsx
    Commented Apr 21, 2021 at 23:40

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