6.034 Artificial Intelligence - Recitations, fall 2004 online slides on search
	Power of f If a heuristic function is wrong (bad estimate), it either overestimates (guesses too high) or underestimates (guesses too low). For A*, overestimating is much worse than underestimating. A* returns an optimal answer if h(n) is admissible, or never overestimates the true cost to the nearest goal.