Given two heuristic functions h1(n) and h2(n) , where both h1(n) &le h*(n) and h2(n) &le h*(n) , we say h2(n) is more informed than h1(n) if h2(n) > h1(n) for all nodes n .
Given multiple admissible heuristic functions h1(n), h2(n), ..., the function h(n) = max(h1(n), h2(n), ...) is also admissible and at least as informed as any of its component heuristic functions.
Since heuristic functions can easily be combined in the above manner, it is possible to learn heuristics from experience. The simplest case is remembering the true cost of solving a particular problem. More generally, features of particular problems can be learned along with costs.