Some math symbols don't display on Linux

Hello,

I've just started to look at Amaya for writing mathmatics.

Working through the manual, I find that some of the math symbols (such
as subset) display as a bold digit, rather than the correct symbol.

As this only occurs on Linux (it works fine on MAC OS X), I suspect a
font issue.

Have others encountered this problem, and if so, is there a known solution?