static Pt varyPoint(Pt p, int w, int h) {
  ret tossACoin() ? randomPoint(w, h) : varyPoint(p, 10);
}

static Pt varyPoint(Pt p, int range) {
  range = max(range, 1);
  ret new Pt(
    random_incl(p.x-range, p.x+range),
    random_incl(p.y-range, p.y+range));
}