···3838 number. In particular, [f u = f v] if and only if [u] and
3939 [v] are in the same component. Another property of the
4040 numbering is that components are numbered in a topological
4141- order: if there is an arc from [u] to [v], then [f u >= f u]
4141+ order: if there is an arc from [u] to [v], then [f u >= f v]
42424343 Not tail-recursive.
4444 Complexity: O(V+E)