2 % mmrests of second voice should not disappear
4 % the problem is more complex: the mmrest-engraver lives at staff level,
5 % but it seems that we need one per voice.
9 \context Staff = Viole <
10 \context Voice=one \partcombine Voice
11 \context Thread=one \relative c''{ R1 d4 d d d }
12 \context Thread=two { R1*2 }
19 \remove Multi_measure_rest_engraver;
24 \consists Multi_measure_rest_engraver;
25 \consists Bar_engraver;