Sorry, in my reply, the sample coding got "auto formatted" because the the
note b after < was interpreted as bold tag and everything went belly-up.
I've now inserted a space between < and b and the LilyPond code became
readable:
\version "2.19.81"
\relative {
<<
{ \autoBeamOff e''16*2 e e
Hi Andy,
You don't need a special function for this, it's all contained in the
standard.
I've constructed a parallel context (with <<...\\...>>) thus having two
voices with opposite stem directions.
The upper noteheads will automatically be merged.
Now for the tricky part (the 16th flags):
