I have often to write chemical formulas, e.g.:

NH_4 Cl + H_2 O "<->" HCl + OH^"-" + NH_4 ^"+"

this arrow ("<->") should be like in this wiki-article:
Gleichgewichtspfeil

It would be extremly useful to implement this, because rightarrow or dlrarrow are not the same

edit: I don't want to replace any arrow. I want to add this arrow - and its not the same as the arrow for resonance (I'm sorry, couldn't find it in the english wiki):
"Dies wird durch den Mesomeriepfeil (Resonanzpfeil) ↔ symbolisiert, der nicht mit dem ein chemisches Gleichgewicht symbolisierenden Doppelpfeil \;\leftrightharpoons\; verwechselt werden darf." http://de.wikipedia.org/wiki/Mesomerie

means: the arrow for resonance may not be mixed up with the arrow for chemical equilibrium

when I use openoffice.org for math projects, I use OO.org formula to make formulas. but whet i look in applications >office> I can't find oo.org formula, how ever when i edit system>prefences>main menu I can edit it so i can find oo.org formula.

To edit formulas is really difficult...
It would be really helpful, if you could edit the formulas like in MS Office.