Yet another dynamic Y combinator

dynamicY.cs

delegate dynamic D(dynamic d);

static async Task Main()
{
    Func<D, D> selfApp = f => f(f);
    var Y = (Func<D, D> f) => selfApp(g => f(x => g(g)(x)));

    Func<D, D> fact = (D f) => n => n <= 1 ? 1 : n * f(n - 1);
    Console.WriteLine(Y(fact)(5));
}