Y combinator in F# and C#

y-combinator-fsharp.fs

let protoFib f x = if x > 1 then f(x-1) + f(x-2) else x
let rec Y f x = f (Y f) x
let fib = Y protoFib
[1..10] |> List.map fib |> printfn "%A" 

y-combinator.cs

void Main()
{
	Fib(10).Dump();
}

int Fib(int n)
{
	return Y<int,int>(ProtoFib, n);
}

// attempt at Fibonacci function
int ProtoFib(Func<int,int> f, int x) {
	return x > 1 ? f(x-1) + f(x-2) : x;
}

// attempt at factorial function
double ProtoFactorial(Func<int, double> f, int x)
{
	return x > 1 ? x * f(x-1) : 1;
}

U Y<T,U>(Func<Func<T, U>, T, U> f, T x) {
	var Yf = new Func<T, U>(t => Y(f, t));
	return f(Yf, x);
}

y-combinator2.cs

void Main()
{
	var Fib = Y<int,int>(ProtoFib);
	Fib(10).Dump();
}

int ProtoFib(Func<int,int> f, int x) {
	return x > 1 ? f(x-1) + f(x-2) : x;
}

Func<T,U> Y<T,U>(Func<Func<T, U>, T, U> f) {
	var Yf = new Func<T, U>(t => Y(f)(t));
	return new Func<T,U>(x => f(Yf, x));
}