ADD_ACKNOWLEDGER (Spacing_engraver, staff_spacing);
ADD_ACKNOWLEDGER (Spacing_engraver, note_spacing);
ADD_ACKNOWLEDGER (Spacing_engraver, rhythmic_head);
ADD_ACKNOWLEDGER (Spacing_engraver, staff_spacing);
ADD_ACKNOWLEDGER (Spacing_engraver, note_spacing);
ADD_ACKNOWLEDGER (Spacing_engraver, rhythmic_head);