def delete(tuple)
      key = bin_key(tuple)
      bin = @hash[key]
      return nil unless bin
      bin.delete(tuple)
      @hash.delete(key) if bin.empty?
      tuple
    end
def delete(tuple)
      key = bin_key(tuple)
      bin = @hash[key]
      return nil unless bin
      bin.delete(tuple)
      @hash.delete(key) if bin.empty?
      tuple
    end
Removes +tuple+ from the TupleBag.