[(0,1),(1,2),(0,3),(3,4),(1,5),(4,6),(3,7),(2,8),(7,9),(6,9),(5,10),(10,11),(9,12),(7,13),(2,14),(5,15),(4,16),(8,17),(8,18),(6,19),(10,20)]
[(0,1),(1,2),(2,3),(1,4),(3,5),(0,6),(4,7),(5,8),(2,8),(3,9),(6,10),(9,11),(5,12),(7,13),(7,14),(4,15),(8,16),(10,17),(9,18),(10,19),(6,20)]
