# Trying to use FreeSerif as a maths font — what am I doing wrong?

Always in search of the ideal font combination unicorn, I thought I'd try the GNU Free UCS Outline Fonts (FreeSerif, FreeSans, and FreeMono). I seem to have fallen at the first hurdle:

\documentclass[final]{article}
\usepackage{fontspec}
\setmainfont{FreeSerif}
\usepackage{unicode-math}
\setmathfont{FreeSerif}
\begin{document}
$x+y=\sqrt{z}$
\end{document}

Both XeLaTeX and LuaLaTeX (.otf format fonts with TexLive, Windows 7) give me this:

What am I missing?

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This is not an answer but to help, here is using XeTeX img819.imageshack.us/img819/9996/shutterseleo006.png and here using LuaLaTeX img267.imageshack.us/img267/7355/shutterseleo007.png on my Lubuntu 11.10 with TexLive2011. – Sigur Feb 10 '13 at 13:38
@Sigur Is that using the .otf version? (I'm on Windows 7) – Brent.Longborough Feb 10 '13 at 13:45
Hum, sorry. I checked it now and I have those fonts in .ttf format. But I don't know if TeXLive uses them. – Sigur Feb 10 '13 at 13:51
You can't use FreeSerif as a math font because it lacks a MATH table. Both XITS Math and TG Termes Math have the table and are based, like FreeSerif, on Times. – egreg Feb 10 '13 at 13:55
In Classic TeX (and apparently a fallback in xetex) the thickness of the rule in \sqrt is given by the height of the sqrtsign character, so TeX fonts have a sqrtsign with large depth making tex math fonts unusable in other systems. The math table can specify this without needing to corrupt the glyph positioning. – David Carlisle Feb 10 '13 at 14:05