srecord PosNegScore(double pos, double neg) implements Comparable<PosNegScore> {
  double diff() { ret pos-neg; }
  
  public int compareTo(PosNegScore s) { ret cmp(diff(), s.diff()); }
  
  toString {
    if (neg == 0) ret pos == 0 ? "0" : "+" + pos;
    if (pos == 0) ret "-" + neg;
    ret "+" + pos + "/-" + neg;
  }
}