public final boolean unlink(DragObject<?, ?, ?> object,
			DropTarget<?, ?, ?> target) {
		final Track t = (Track) object;
		final MidiInstrumentDropTarget i = (MidiInstrumentDropTarget) target;
		final Set<Integer> set = this.instrumentToTrack.get(target);
		set.remove(t.getId());
		if (set.isEmpty()) {
			this.instrumentToTrack.remove(i);
			return true;
		}
		return false;
	}