Others have answered other aspects of this, but as I understand it, it is not the case that we don&#x27;t know how rare they (BH-BH events) are because they are so rare, we don&#x27;t know how rare they are, because we don&#x27;t have a really good model for them. So, we don&#x27;t know how often we&#x27;d expect to detect them, once we had a detector.