!7

static Canvas canvas;
static CirclesAndLines cal;

p-subst {
  Pair<CirclesAndLines, Canvas> p = showWeb(randomWeb());
  cal = p.a;
  canvas = p.b;
  addButtonsToWindow2(canvas, "Next", r {
    CirclesAndLines newCAL = webToCAL(randomWeb());
    canvas = showCAL_2(newCAL, cal, canvas);
  });
}