static Map<Pair<S>, Bool> ai_isRuleSuitableForFunction_cache = synchroHashMap();

static bool ai_isRuleSuitableForFunction(S rule, S f) {
  Pair<S> p = pair(rule, f);
  Bool b = ai_isRuleSuitableForFunction_cache.get(p);
  if (b != null) ret b;
  pcall {
    try {
      callAndMake(f, rule, null);
      ai_isRuleSuitableForFunction_cache.put(p, true);
      true;
    } catch (UnsuitableRuleException e) {
      ai_isRuleSuitableForFunction_cache.put(p, false);
      false;
    }
  }
  throw new FunctionIsBroken;
}