forwardDifference(x(1), n) := forwardDifferenceHelper(x, n, [x]);

forwardDifferenceHelper(x(1), n, result(2)) :=
	let
		difference := tail(x) - x[1 ... size(x) - 1];
	in
	result when n = 0 or size(x) = 1 else
	forwardDifferenceHelper(difference, n - 1, result ++ [difference]);