def encode_nested_bytes(item)
      if item.instance_of?(String)
        return item if item.size == 1 && item.ord < PRIMITIVE_PREFIX_OFFSET
        prefix = length_prefix item.size, PRIMITIVE_PREFIX_OFFSET
      else # list
        item = item.map {|x| encode_nested_bytes(x) }.join
        prefix = length_prefix item.size, LIST_PREFIX_OFFSET
      end

      "#{prefix}#{item}"
    end
def encode_nested_bytes(item)
      if item.instance_of?(String)
        return item if item.size == 1 && item.ord < PRIMITIVE_PREFIX_OFFSET
        prefix = length_prefix item.size, PRIMITIVE_PREFIX_OFFSET
      else # list
        item = item.map {|x| encode_nested_bytes(x) }.join
        prefix = length_prefix item.size, LIST_PREFIX_OFFSET
      end

      "#{prefix}#{item}"
    end
RLP encode (a nested list of ) bytes.