Symbol "is proportional to"

Hallo all,

I need to include some mathematical formulae in my RoboHelp 8 CHM file, and have problems with the symbol "is proportional to".

I can get it to display using Symbol font and Alt-0181 (usually the "micro" symbol) but if I open the HTML using Firefox this does not work.

The Unicode abbreviation is ∝ but RoboHelp refuses to accept this, when I insert it in HTML view it converts it to ∝ when I switch back to Design view.

RoboHelp will accept ∝ but IE7 and the CHM viewer fail to display it (Firefox is just fine). The image below summarises the situation.

Note that my SME seems to have incorrectly used "infinity" where he means "proportional"; when he gets back from holiday I'll square that with him. My readers are mathematically literate and will probably see through the mistake and read the formula correctly.

So my options are:
* use Symbol Alt-0181 knowing it will go wrong if we ever go over to WebHelp and Firefox;
* use "infinity" and hope that my readers will forgive me;
* use GIFs and accept the loss of quality

Or does anybody know a way of showing this symbol reliably?

--- Derek