sclass RandomAndVary_Int implements RandomAndVary<Int> {
  int min = 0, max = 255; // inclusive
  double varyFactor = 0.1;
  
  public Int randomInstance() { ret random(min, max+1); }
  public Int varyInstance(Int a) {
    ret clipInt(min, max, iround(a+(max-min)*varyFactor));
  }
}