csharp fixpoint fib

fib.cs

using System;

public class Program
{
    delegate T id<T>(T arg0);

    static id<T> Y<T>(id<id<T>> f)
    {
        //Y f = f ( Y f )
        return x => f(Y(f))(x);
    }

    static id<id<T>> _<T>(id<id<T>> f) { return f; }

    public static void Main(string[] args)
    {
        var fib = _<int>(f => n => n < 2 ? n : f(n - 1) + f(n - 2));
        Console.WriteLine(Y(fib)(5));
    }
}