Trouble customizing Theorem with LaTeX Includes

[eschirmacher]

Description

Hello!

I'm using Quarto to write a book. Using version 1.7.31 on Windows with a full installation of TeXLive.

I want to customize how theorems are rendered in PDF. Looking at the documentation for LaTeX Includes and reading that it would include my LaTeX commands "at the end of the header" I added a few commands inside include-in-header: within the file _quarto.yml. The relevant portion looks like this:

format:
  pdf:
    documentclass: scrreprt
    keep-tex: true
    include-in-header:
      - text: |
          %%%%%
          %%%%% Start user commands
          %%%%%
          \usepackage{amsthm}
          \definecolor{CASBlue}{rgb}{0.00,0.00,0.80}
          \newtheoremstyle{casthm}%
          {3pt}{3pt}%
          {\itshape}%
          {0pt}{\color{CASBlue}\sffamily\bfseries}%
          {.}%
          { }%
          {\thmname{#1}\thmnumber{ #2}\thmnote{ (#3)}}%
          \theoremstyle{casthm}
          \newtheorem{theorem}{Theorem}[chapter]
          %%%%%
          %%%%% End of user commands
          %%%%%

I tried to render to PDF, but got a nasty error message during the xelatex compilation:

compilation failed- error
LaTeX Error: Command \theorem already defined.
               Or name \end... illegal, see p.192 of the manual.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...

l.239 \newtheorem{theorem}
                          {Theorem}[chapter]

Looking at the generated TeX file (attaching it here with extension txt, as extension tex is not supported tmp-minimal-header.txt), the problem is clear. My included commands are in lines 182 through 198. But further down, on lines 237 to 239, we have

\usepackage{amsthm}
\theoremstyle{plain}
\newtheorem{theorem}{Theorem}[chapter]

The documentation line saying "contents will be included at the end of the header" does not mean at "the end of the LaTeX preamble." There are a lot more LaTeX commands after my included code.

I have tried to trace back how lines 237 to 239 were inserted there, but have not yet succeeded. I managed to understand that most of the LaTeX preamble is generated via LaTeX Partials, but I cannot yet see which partial is responsible for adding these three lines. If I knew which partial generated these lines, I could create a replacement with my definitions and use that.

Any suggestions as to which partial might be responsible would be greatly appreciated. Or perhaps a different way of customizing theorems.

Thank you very much!

Ernesto

[mcanouil]

You need to use the proper LaTeX command to overwrite what Quarto is adding but you won't be able to replace it without post-processing the LaTeX file then manually compile it to PDF.
Overwriting, the theorem defined by Quarto is at the risk of breaking features such as cross-reference.

• https://github.com/quarto-dev/quarto-cli/blob/10af0a2ddcd4134a2d2bc9b3f7a20233e0f81ba3/src/resources/filters/crossref/theorems.lua

[eschirmacher]

Thank you very much for pointing to the file theorems.lua. Very helpful.

I can see how the interesting bit of the LaTeX preamble is assembled in this lua file. What I do not see is how the different types of constructs (thm-, def-, cnj-, etc...) get assigned a style. Theorems and conjectures get style plain, but definitions get style definition.

Would you happen to know if it might be possible to provide a style, say casthm in a qmd file so that theorems.lua generates

\theoremstyle{casthm}
\newtheorem{theorem}{Theorem}[chapter]

instead of

\theoremstyle{plain}
\newtheorem{theorem}{Theorem}[chapter]

[mcanouil]

That's not possible.
As I said, it's either post-processing or trying to overwrite.

The styles are defined in the following file, but you don't have access to it from a Quarto document.

• https://github.com/quarto-dev/quarto-cli/blob/10af0a2ddcd4134a2d2bc9b3f7a20233e0f81ba3/src/resources/filters/customnodes/theorem.lua

[eschirmacher]

Thank you very much for referencing theorem.lua, and it's unfortunate that this information has been hard-coded.

I appreciate your help and insights on this matter.

[eschirmacher]

I found a way to customize a theorem, definition, conjecture, etc... by inserting LaTeX code in two places:

1. Inside a include-in-header LaTeX includes to create new theorems, definitions, conjectures, etc... in a different style, and
2. Using the title.tex LaTeX partial to redefine theorem, definition, conjecture, etc... to use the newly defined environments in the previous step.

In your _quarto.yml add template partials and LaTeX code as follows:

format:
  pdf:
    documentclass: scrreprt
    keep-tex: true
    template-partials:
      - title.tex
    include-in-header:
      - text: |
          \usepackage{amsthm}
          \definecolor{CASBlue}{rgb}{0.00,0.00,0.80}
          \newtheoremstyle{specialthm}%
          {3pt}{3pt}%
          {\itshape}%
          {0pt}{\color{CASBlue}\sffamily\bfseries}%
          {.}%
          { }%
          {\thmname{#1}\thmnumber{ #2}\thmnote{ (#3)}}%
          \theoremstyle{specialthm}
          \newtheorem{specialtheorem}{Theorem}[chapter]
          \newtheorem{specialdefinition}{Definition}[chapter]

Create a new file, title.tex, in the same directory as your _quarto.yml file with the following contents:

\renewenvironment{theorem}{\begin{specialtheorem}}{\end{specialtheorem}}
\renewenvironment{definition}{\begin{specialdefinition}}{\end{specialdefinition}}

$if(title)$
\title{$title$$if(thanks)$\thanks{$thanks$}$endif$}
$endif$
$if(subtitle)$
\usepackage{etoolbox}
\makeatletter
\providecommand{\subtitle}[1]{% add subtitle to \maketitle
  \apptocmd{\@title}{\par {\large #1 \par}}{}{}
}
\makeatother
\subtitle{$subtitle$}
$endif$
$-- This supports Quarto's authors normalization
\author{$for(authors)$$it.name.literal$$sep$ \and $endfor$}
\date{$date$}

The first two lines redefine the theorem and definition environment. The remaining lines of code are from the original title.tex file that is located in Quarto/share/formats/pdf/pandoc/ (my Windows installation).
Please make sure your document uses both of these environments. Otherwise, you will get a LaTeX error during compilation.

With these changes, your theorems and definitions will be blue colored and in a sans serif, bold font.

I'm sure that there is a more elegant way to accomplish this, but at least it solves my current problem.