[O] How to use jsMath with org-mode

[Joseph Vidal-Rosset]

http://orgmode.org/worg/org-tutorials/org-jsmath.html

Hello the list,

I have followed this tutorial, but unfortunately, I do not understand why
the command \ref  meets always the error message : "Undefined control
sequence" . I do not succed to get on html page references to numbered
equations.

Does someone can help me?

Best wishes

Jo.