static <A> A lambdaMapLike applyUntilEqual_goOneBackOnNull(IF1<A> f, A o) {
  while ping (true) {
    A o2 = f.get(o);
    if (o2 == null || eq(o, o2)) ret o;
    o = o2;
  }
}

static <A> A lambdaMapLike applyUntilEqual_goOneBackOnNull(A o, IF1<A> f) {
  ret applyUntilEqual_goOneBackOnNull(f, o);
}