Key: 1.Re8! waiting.

1…Kxb6 2.Bd8 mate

1…Kb4 2.Bd2 mate

1…Kd6 2.Bf4 mate

1…Kd4 2.Bf6 mate

The four Black king flights form a star pattern and are known in problem parlance as star-flights. Note also that the key gives the black king an extra flight on b6. Such flight-giving keys are especially prized by composers.