EacchEach node <code>v</code> is assigned a unique integer <code>v.index</code>, which numbers the nodes consecutively in the order in which they are discovered. It also maintains a value <code>v.lowlink</code> that represents the smallest index of any node known to be reachable from <code>v</code> through <code>v</code>'s DFS subtree, including <code>v</code> itself. Therefore <code>v</code> must be left on the stack if <code>v.lowlink < v.index</code>, whereas v must be removed as the root of a strongly connected component if <code>v.lowlink == v.index</code>. The value <code>v.lowlink</code> is computed during the depth-first search from <code>v</code>, as this finds the nodes that are reachable from <code>v</code>.
