using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        List<int> list = new() { 1, 2, 3 };

        //List<int> list = new() { 1, 2, 3, 4, 5, 6, 7, 8, 9 };

        var emptyCollection = Enumerable.Empty<IEnumerable<int>>();

        var emptyCombination = Enumerable.Empty<int>();

        IEnumerable<List<int>> combinations = list

            .Aggregate(emptyCollection.Append(emptyCombination),

                ( acc, next ) => acc.Concat(acc.Select(entry => entry.Append(next))))

            .Skip(1) // skip the initial, empty combination

            .Select(comb => comb.ToList());

        foreach (var comb in combinations.OrderBy(c => c.Count).ThenBy(c => c.Sum()))

        {

            Console.WriteLine(string.Join(" ", comb));

        }

    }

}