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