C# 7 Local Function example with tuples in a tail call

Program.cs

using System;

// Visual Studio 15 Preview 3
// Conditional compilation symbols:  __DEMO__ ,__DEMO_EXPERIMENTAL__
// Manually added ValueTuples.cs to project https://raw.githubusercontent.com/dotnet/roslyn/future/docs/features/ValueTuples.cs
namespace TupleExamples
{
    class Program
    {
        static void Main(string[] args)
        {
            long Factorial(int x)
            {
                long Aux((int acc, int n) a)
                {
                    if (a.n <= 1) return a.acc;
                    
                    var r = (a.acc * a.n, a.n - 1);
                    return Aux(r);
                }

                (int, int) t = (1, x);
                return Aux(t);
            }

            Console.WriteLine($"1! = {Factorial(1)}");
            Console.WriteLine($"5! = {Factorial(5)}");
            Console.WriteLine($"20! = {Factorial(20)}");

            Console.ReadKey();
        }
    }
}

Same code as https://gist.github.com/MikeMKH/7488b5ce907bb58912f7d4d476ebdf48 but playing with defining the Tuples types.