feta chars in latex

[Graham Percival]

How does one use feta characters inside LaTeX (as part of
lilypond-book)?  I'd like to include some performance notes, including
segno and flat.  If I was doing it inside a lilypond header, I know I
could do \fetachar\fetasegno and \fetachar\fetaflat, but when I try
that within the LaTeX portion of the lilypond-book file, it complains
about

...
! Undefined control sequence.
l.26 \fetachar
              \fetasegno
? q


(to be more exact, this error occurs when I run "latex foo.latex", after
I've successfully run "lilypond-book foo.tex", on OSX 10.3 with LilyPond
2.0.1)

I'm guessing that I'm missing something simple here, but I can't find
the proper command.

- Graham