Slurs

[Andrew Sidwell]

I'm writing out the Brahms Cradle song (Wiegenlied, Op. 48 No. 2) in 
Lilypond, and there's a part where there's a note tied to two 16th grace 
notes.  I was expecting

af4 ( \grace { bf16 [af16] } )

to work, but that just errors on me.  Any ideas?

Cheers,
Andrew Sidwell