def delete_unless_alive
      deleted = []
      @hash.each do |key, bin|
        bin.delete_if do |tuple|
          if tuple.alive?
            false
          else
            deleted.push(tuple)
            true
          end
        end
      end
      deleted
    end
def delete_unless_alive
      deleted = []
      @hash.each do |key, bin|
        bin.delete_if do |tuple|
          if tuple.alive?
            false
          else
            deleted.push(tuple)
            true
          end
        end
      end
      deleted
    end
Delete tuples which dead tuples from the TupleBag, returning the deleted
 tuples.