Figure 6

Tree building algorithm comparison. Comparison of initial tree build algorithms. Union is the Wagner algorithm + RAS + Union-pruning. Union - Look. 4 is the Wagner algorithm + RAS + Union-pruning + Lookahead of at most 4 trees. Look. 10 is the Wagner algorithm + RAS + Lookahead of at most 10 trees. MST is the Wagner algorithm + MST sequence, but no Union-pruning. Union-MST-Look. 2 is the Wagner algorithm + MST sequence + Union-pruning + Lookahead of at most 2 trees.