Neat and related: When writing HTML with some math, I don't really want to write MathML by hand (let alone depend on MathJax or something like that). LaTeXML turns out to be helpful again, specifically via the latexmlmath (which btw. can be used above as well, and is faster). Either way, I have quickly hacked together a function that uses latexmlmath to convert TeX-math in a comment into MathML:

(defun mathml-from-tex ()
  "Convert TeX in a comment to MathML in a buffer.
The TeX has to be written in a single-line comment prefixed with a
\"MathML:\" string.  For example:

  <!-- MathML: \frac{-b \\pm \\sqrt{b^2 -4ac}}{2a} -->

Everything until the end of the comment (or line) is passed to
\"latexmlmath\" (part of the LaTeXML suite) and injected into the next
line of the buffer.  A comment indicating the end of the math block is
also added, so that multiple invocations of the command can replace the
old output."
  (interactive)
  (save-excursion
    (goto-char (line-beginning-position))
    (unless (search-forward-regexp
	     (rx (literal comment-start) (* space)
		 "MathML: " (group (* nonl))
		 (literal comment-end))
	     (line-end-position) t)
      (user-error "No instruction found"))
    (if (eobp)
	(insert "\n")
      (forward-line 1))
    (let ((end "EndOfMathML")		;TODO: use </math>
	  (math (match-string 1))
	  (start (point)))
      (when (search-forward-regexp (rx (literal end)) nil t)
	(delete-region start (line-end-position)))
      (save-excursion
	(insert end)
	(save-excursion
	  (insert (if (eolp) "" "\n")))
	(comment-line 1))
      (call-process-region math nil "latexmlmath" nil t t "-"))))

I also attach a quick demo, see below.

@mhagmuller Hatte vor vielen Jahren selbst die fragwürdige Ehre, sowohl via Word als auch via #LaTeX diverse Konferenz-Proceedings technisch zu erstellen.

Man muss hier nicht extra betonen, wie viel mehr Schmerz das mit #Word war. Aber auch bei LaTeX war der Aufwand nicht unerheblich.

Persönliches Highlight: ein Prof schickte doch tatsächlich sein Paper als ein doc-File (damals noch ohne "x") für ein (LaTeX-)Proceeding, das er einfach bei der Dateiendung auf ".tex" änderte.

Si il y'en a qui sont au courant, je cherche un moyen d'utiliser #emacs natif sous android (pas la version console termux) + #termux + #termuxapi.

Pour les deux premiers, j'ai trouvé des builds spéciaux d'emacs et termux avec des apk signés par la même clef. Ça permet à emacs de pouvoir utiliser des programmes installés via termux (pkg install xxx), utils pour plein de fonctionnalité (#gnuplot, #gnupg, export #latex pdf, #git, etc..).
https://sourceforge.net/projects/android-ports-for-gnu-emacs/files/termux/

Par contre, je n'ai pas trouvé d'apk de termux-api avec cette même clef. Si il y a rien, je vais devoir déconstruire l'apk et la re-signer avec la bonne clef, mais j'aimerai éviter si c'est possible..

@KathyReid Have used other platforms like Google Docs with LaTeX documents but indeed it’s not the same. Or using version control with git, but again it’s not the same: no simultaneous editing plus comments (although when careful to write each sentence in its own line, git works very well for collaborative manuscript editing in your favourite text editor). Would like to know of alternatives too.
#LaTeX