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