-ADD_ACKNOWLEDGER(Volta_engraver, staff_symbol);
-ADD_ACKNOWLEDGER(Volta_engraver, note_column);
-ADD_ACKNOWLEDGER(Volta_engraver, bar_line);
+ADD_ACKNOWLEDGER (Volta_engraver, staff_symbol);
+ADD_END_ACKNOWLEDGER (Volta_engraver, staff_symbol);
+ADD_ACKNOWLEDGER (Volta_engraver, note_column);
+ADD_ACKNOWLEDGER (Volta_engraver, bar_line);