using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        /*

        public static TSource Aggregate<TSource>(this IEnumerable<TSource> source, 

                                         Func<TSource, TSource, TSource> func);

​

        public static TAccumulate Aggregate<TSource, TAccumulate>(this IEnumerable<TSource> source, 

                                         TAccumulate seed, 

                                         Func<TAccumulate, TSource, TAccumulate> func);

​

        public static TResult Aggregate<TSource, TAccumulate, TResult>(this IEnumerable<TSource> source, 

                                         TAccumulate seed, 

                                         Func<TAccumulate, TSource, TAccumulate> func, 

                                         Func<TAccumulate, TResult> resultSelector);

        */

        IList<string> strList = new List<string>() { "One", "Two", "Three", "Four", "Five" };

        var commaSeperatedString = strList.Aggregate((s1, s2) => s1 + ", " + s2);

        Console.WriteLine(commaSeperatedString);

    }

}