how to slur grace note with previous note?

[Bodo]

Hi,

Every piece of documentation about grace notes I have found so far connects
the grace note with the normal note that follows it.
However, I want to add two grace notes that are sung on the same syllable as
the previous note, and hence they should be connected with a slur to the
previous note.

Consider this fragment:

a'4 \grace { b'16 [a'16] } g'4 

This places the grace notes b and a close to the g. There are no slurs. I
want to grace notes close to the a.

The next thing is almost what I want:

a'4 \appoggiatura { b'16 [a'16] } g'4 

Here slurs are drawn, but between the last 3 notes, not the first three.

What I'm trying to get is something like this:

a'4 ( \grace { b'16 [a'16] } )    g'4 

However, this produces an error "unexpected ')'". Is it possible to
associate grace notes to the note preceding them and connect them with a
slur?

 Bodo