The semantics is as follows: under an optimistic estimate h(n) (= underestimating costs or overestimating merits) the total cost (the overall quality) for solving ACROSTIC GENERATION via a path along node n is always larger (smaller) than f (n).
g(n) accumulates the true cost (the achieved quality) for the partial acrostic via a concrete path s = n 0 , n 1 , .