static void ai_gc_clear() {
  int n = 0;
  for ping (WebRelation rel : indexedRelations("has GC distance")) {
    if (ai_isTripleWeb(rel.web)) {
      ai_invalidateWeb(rel.web);
      ++n;
    }
  }
  if (n != 0) print("Cleared " + n(n, "GC entry"));
}