\version "2.19.61"
\language "english"
hideOneNote = {
\once \omit Stem
\once \omit Flag
}
\relative {
\key ef \major
\time 3/4
<<
{
| f''4-> s2
| d4
}
\\
{
| r8 f, ^( <e g> <ef a> <d bf'> <c c'>
% \stemUp % doesn't help
| << \hideOneNote d'8 ) r >> % works, emits warning
%| << \hide Stem \hide Flag d'8 ) r >> % works, emits warning
%| << \hideNotes d'8 ) \unHideNotes r >> % doesn't work
}
>>
}
-------------------------------