[AUCTeX] Forcing indentation in math environments

[Julien Cubizolles]

I want to control indentation in math environments. I've defined the
following function

--8<---------------cut here---------------start------------->8---
(defun jc-math-mode-indent ()
  "Force indentation in math mode. "
  (interactive "p")
    ;; (delete-horizontal-space)
  (cond
   ((equal current-prefix-arg nil)
    (indent-relative))
   )

  )
--8<---------------cut here---------------end--------------->8---

used in LaTeX-environment-list:

--8<---------------cut here---------------start------------->8---
(("verbatim" current-indentation)
 ("verbatim*" current-indentation)
 ("array" jc-math-mode-indent)
 ("displaymath" jc-math-mode-indent)
 ("eqnarray" jc-math-mode-indent)
 ("eqnarray*" jc-math-mode-indent)
 ("equation" jc-math-mode-indent)
 ("equation*" jc-math-mode-indent)
 ("picture")
 ("tabbing")
 ("table")
 ("table*")
 ("tabular")
 ("tabular*")
 ("code")
 ("tikzpicture")
 ("pspicture")
 ("align" jc-math-mode-indent)
 ("align*" jc-math-mode-indent)
 ("table")
 ("tabular")
 ("pspicture")
 ("tikzpicture")
 ("axis")
 ("psgraph")
 ("maple")
 ("figure")
 ("scope"))
--8<---------------cut here---------------end--------------->8---

It behaves the way I want:
TAB indents relative to the previous line
C-u TAB aligns with the previous line.

The thing is I'm not sure why it's working :-) since strange things also
happen:

* If yas-minor-mode is on, the point is at the beginning of the text
  after using TAB, which is what I want; it's at the beginning of the
  line if yas is not on. I could choose something else than TAB for
  yas-expansion but this side-effect is actually what I prefer

* I don't see why the (cond ...) is needed but it is: C-u TAB behaves
  the same as TAB otherwise, as if I used indent-relative instead of my
  custom function.

* If I try to add (delete-horizontal-space) (commented out for now), TAB
  acts as C-u TAB.

Any idea how to properly achieve:
* TAB does indent-relative
* C-u TAB aligns with the previous line
* C-u n TAB does indent-relative n times

with point remaining at the same position in the text, regardless of yas
being on or off ?

Thanks.