sclass PtTree {
  Node root = new Leaf;
  
  abstract class Node {
    Node parent;
    
    abstract bool add(Pt p);
    abstract void collectPointsIn(Rect r, L<Pt> out);
  }
  
  class Leaf extends Node {
    Cl<Pt> points;
  }
  
  class Split extends Node {
    int splitPoint;
    Node a, b;
  }
  
  class SplitH extends Split {}
  class SplitV extends Split {}
  
  int maxPointsPerNode = 4;
  
  bool add(Pt p) {
    ret root.add(p);
  }
  
  L<Pt> pointsIn(Rect r) {
    new L<Pt> out;
    root.collectPointsIn(r, out);
    ret out;
  }
}