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