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