* Issue 1: custom symbols not exported
I am trying to export this to ODT without much
success (it exports well to PDF through LaTeX, and
the previews are fine).

This equation is exported correctly:
\[ a = 2 \]

This too.
\[ a = \frac{1}{2} \]

But this isn't.
\[ a = \deriv{x}{X} \]

The definition of deriv{}{} is in
the [[./symbols.tex][attached file]], and the preview seems to work
too (scale and symbol)

* Issue 2: when exported, resolution is unchanged
  I have tried to change the resolution of the
  exported image, but dvipng seems to disregard
  it.

* Configuration                                    :noexport:
  I have this configuration (I just open the
  file). It asks me if I want to apply the "usafe"
  scale variable.
** Emacs configuration
   #+BEGIN_SRC emacs-lisp :results none
     (require 'package)
     (package-initialize)
     (use-package "org")
     (setq org-export-backends '(latex odt))
     (org-babel-do-load-languages 
	'org-babel-load-languages  
	'((shell . t)
	  (emacs-lisp . t)))
   #+END_SRC
*** My system version
    #+BEGIN_SRC emacs-lisp
      (org-version)
    #+END_SRC

    #+RESULTS:
    : 9.0.7

    #+BEGIN_SRC emacs-lisp
      (emacs-version)
    #+END_SRC

    #+RESULTS:
    : GNU Emacs 24.4.1 (x86_64-pc-linux-gnu, GTK+ Version 3.4.2)
    :  of 2015-01-11 on maritornes, modified by Debian

** Cleaning
   Before I do C-c C-e o o, I run this:
   #+BEGIN_SRC shell :results none
     rm -fr ltx{png,img}
   #+END_SRC

** General options
   - Load symbols
     #+LaTeX_HEADER: \input{./symbols.tex}

   - No table of contents
     #+OPTIONS: toc:nil
** Change the resolution of the exported equations (and previews)
   - Export (and preview) the equations as pictures
     The equation looks terrible with
     #+OPTIONS: tex:imagemagick

     There is a decent picture with dvipng, but I
     cannot improve it (uncomment if necessary)
     # #+OPTIONS: tex:dvipng

   - Improve the quality of the pictures (does not work)
     I just want to export; previewing with a
     different scale is an undesired side-effect
     # https://stackoverflow.com/a/20033865
     # Local Variables:
     # org-format-latex-options: (plist-put org-format-latex-options :scale 10 :foreground default :background default)
     # End:

    - This does not work either for the export (it
      does for preview):
     # org-format-latex-options: (:scale 10 :foreground default :background default)

    - I have also tried with
      M-x customize-variable org-format-latex-options