edges: 0-1 0-2 0-3   order: 0 1 2 3
edges: 0-1 0-2 0-3 1-2   order: 0 1 2 3
edges: 0-2 0-3 1-3   order: 0 2 3 1

connected graphs on 4 labeled vertices reachable from 0: 38
of those, DFS order = BFS order in 26 of them
