using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    static IEnumerable<IEnumerable<T>> GetKCombs<T>(IEnumerable<T> list, int length) where T : IComparable

    {

        if (length == 1) return list.Select(t => new T[] { t });

        return GetKCombs(list, length - 1)

        .SelectMany(t => list.Where(o => o.CompareTo(t.Last()) > 0), 

            (t1, t2) => t1.Concat(new T[] { t2 }));

    }

    public static void Main()

    {

        var input = new List<int>() {1, 2, 3, 4};

        GetKCombs(int)

    }

}