Ошибка: Не удалось найти имя типа или пространства имен "StreamWriter" - C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
 
namespace ConsoleApplication22
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] kniga = new string[26];
            kniga[0] = "\u0061";
            kniga[1] = "\u0062";
            kniga[2] = "\u0063";
            kniga[3] = "\u0064";
            kniga[4] = "\u0065";
            kniga[5] = "\u0066";
            kniga[6] = "\u0067";
            kniga[7] = "\u0068";
            kniga[8] = "\u0069";
            kniga[9] = "\u0070";
            kniga[10] = "\u0071";
            kniga[11] = "\u0072";
            kniga[12] = "\u0073";
            kniga[13] = "\u0074";
            kniga[14] = "\u0075";
            kniga[15] = "\u0076";
            kniga[16] = "\u0077";
            kniga[17] = "\u0078";
            kniga[18] = "\u0079";
            kniga[19] = "\u0080";
            kniga[20] = "\u0081";
            kniga[21] = "\u0082";
            kniga[22] = "\u0083";
            kniga[23] = "\u0084";
            kniga[24] = "\u0085";
            kniga[25] = "\u0086";
            kniga[26] = "\u0087";
            Console.WriteLine(kniga[0]);
            Random l = new Random();
            int n = l.Next(1, 26);
            string line = "";
            for (int i = 0; i < n; i += 1)
                using (StreamWriter[/U][/U] j = new StreamWriter(@"C:\temp\111.txt", true, System.Text.Encoding.Default))
                {
                    line = line + kniga[i];
                    j.WriteLine(line);
 
                    j.Close();
 
                }
        }
    }
}