Running Time Analysis

This is really just two topological sorts: $\Theta(n+m)$.

The magic is in the fact that this works at all!

Terminology: forward reachable, backward reachable. If u and v are in the same strongly connected component, then v is both forward reachable and backward reachable from u (and vice versa).

Argue that G and G^T have the same strongly connected components.

What can we say about when to nodes in the same strongly connected component turn black (with respect to top-level calls to Visit)?