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