@Override
    public String toString() {
        // StringBuffer s = new StringBuffer();
        StringBuilder s = new StringBuilder();
        int counter = 0;
        for (MatterInterval mi : intervals) {
            // [counter]: [MatterInterval]\n
            s.append(counter++);
            s.append(String.valueOf(": "));
            s.append(mi);
            s.append(String.valueOf("\n"));
        }
        return s.toString();
    }