code: def pairwise_point_combinations(xs, ys, anchors):
      
      for i in xs:
          anchors.append((i, max(ys)))
          anchors.append((i, min(ys)))
      for i in ys:
          anchors.append((max(xs), i))
          anchors.append((min(xs), i))
docs: Does an in-place addition of the four points that can be composed by
      combining coordinates from the two lists to the given list of anchors