Many thanks Nick for this help. I am going to inspect my user.el file, in order to correct it, and I will inform you about the result.

Best wishes,

Jo.

Le mar. 12 mars 2019 à 22:34, Nick Dokos <ndokos@gmail.com> a écrit :

Joseph Vidal-Rosset <joseph.vidal.rosset@gmail.com> writes:

> ...
> it  is also  possible to  get sections  in a
> letter with scrlttr2 class. Nevertheless, I have to write the latex code
> \section{}  and I  ignore how  getting  sections via  org-mode for  this
> class. Is it possible to get an org-mode translation for section in this
> class?
>

C-h v org-latex-classes RET

Briefly, you need to add a new element to it, describing what you want org
to do with this class.

Here's a snippet from my init file that adds two latex classes to this
variable. Hope this makes the process clear:

--8<---------------cut here---------------start------------->8---
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; latex export
(setq revtex-class
      '("revtex" "\\documentclass[11pt]{revtex4-1}"
        ("\\section{%s}" . "\\section*{%s}")
        ("\\subsection{%s}" . "\\subsection*{%s}")
        ("\\subsubsection{%s}" . "\\subsubsection*{%s}")
        ("\\paragraph{%s}" . "\\paragraph*{%s}")
        ("\\subparagraph{%s}" . "\\subparagraph*{%s}")))

(setq koma-article-class
      '("koma-article" "\\documentclass[11pt]{scrartcl}"
        ("\\section{%s}" . "\\section*{%s}")
        ("\\subsection{%s}" . "\\subsection*{%s}")
        ("\\subsubsection{%s}" . "\\subsubsection*{%s}")
        ("\\paragraph{%s}" . "\\paragraph*{%s}")
        ("\\subparagraph{%s}" . "\\subparagraph*{%s}")))

(progn
    (require 'ox-latex)
    (add-to-list 'org-latex-classes revtex-class t)
    (add-to-list 'org-latex-classes koma-article-class t)))
--8<---------------cut here---------------end--------------->8---

--
Nick

"There are only two hard problems in computer science: cache
invalidation, naming things, and off-by-one errors." -Martin Fowler