Hello, I've installed the additional (not really entirely free) fonts using the "getnonfreefonts-sys" script in TeX Live.
LyX doesn't offer them in the popup menu in the document settings dialog box however. At least not e.g. Garamond and URW Classico (alias Optima). Luxi Mono however somehow seems to have managed to sneak into the menu. What's up? Sincerely, Wolfgang
