[grumbles]

A clarification:

The opf file contains the following line (as generated by Sigil):

<item href="Fonts/Math2Regular.ttf" id="Math2Regular.ttf" media-type="application/x-font-ttf" />

the css on the other hand contains:

@font-face {
font-family: math2;
font-style : normal, italic;
src : url(../Fonts/Math2Regular.ttf);
}
.infinity { font-family : "math2";
font-weight : 600;
font-size : 125%; }

The space in my previous example was the result of a ham-fisted attempt to manually edit the opf file. I had renamed the file in case the space in the filename was causing the problem. It wasn't. Sigil got it right.

I know that I can use an html entity. I want to use this particular font because I want the specific style of infinity symbol. If use the "infin" entity it works, it just looks bad.

I'm attaching a stripped down version of the epub that demonstrates the problem. I've replaced all the text with "greeked" text. The problem symbol is in the Prologue chapter.