using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var a = new[] { "a", "b" };

        var b = new[] { "1", "2", "3" };    

        List<bool[]> bools = new List<bool[]>();

        for(int i = 0; i < Math.Pow(2, a.Length + b.Length); i++)

        {

            int[] bits = GetBits(i);

            if(bits.Sum() == a.Length)

            {

                bools.Add(bits.Take(a.Length + b.Length).Select(x => x == 1).ToArray());

            }

        }

        foreach(var bo in bools)

        {

        string[] result = new string[a.Length + b.Length];

        int indexa = 0;

        int indexb = 0;

        for(int i = 0; i < result.Length; i++)

        {

            if(bo[i])

            {

                result[i] = a[indexa];

                indexa++;

            }

            else

            {

                result[i] = b[indexb];

                indexb++;

            }

        }

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

        }

    }

    private static int[] GetBits(int num)

    {

        int[] result = new int[32];

        for(int i = 0; i < result.Length; i++)

        {

            if( ((1 << i) & num) > 0)

            {

                result[i] = 1;

            }

        }

        return result;

    }

}