anchor.diff:      newLines.add(new LineSegment(position, this.end));
       return newLines;
     }
  +  
  +  toString() => "($start; $end)";
   }
   
   class LineGroup {
  
positive.code:   LineSegment operator [](int index) => Line[index];
    void insert(int index, LineSegment line) => Line.insert(index, line);
    LineSegment removeAt(int index) => Line.removeAt(index);
  }
  
  List<LineGroup> Lines = new List<LineGroup>();
  
negative.code:   //a[0].visible = false;
    //a[1].visible = false;
    
    List<LineSegment> split2 = b[0].split(intersection);
    print('Split line ${b[0]} intersecting at ${intersection.toString()} into ${split2[0]} and ${split2[1]}');
    b.removeAt(0);
    b.insert(0, split2[0]);
    b.insert(1, split2[1]);
    
    // Hide second part of second line
    b[1].visible = false;
    print(b.toString());
    Lines.add(b);
  }
  
  