if b.ReverseEdges[0].Flag&EdgeFlagsDeleted != 0 {

		var dead, alive int
		for _, e := range b.ReverseEdges {
			if e.Flag&EdgeFlagsBlock != 0 {
				if e.Flag&EdgeFlagsDeleted != 0 {
					dead++
				} else {
					alive++
				}
			}
		}
		if dead > 0 && alive == 0 {