function maximum(lt, num = 0, index = 0) =
    index == len(lt) ? num : (
	    lt[index] > num ? maximum(lt, lt[index], index + 1) : maximum(lt, num, index + 1)
	);

echo(maximum([1,3,5,7,6,4,2]));
echo(max([1,3,5,7,6,4,2])); // OpenSCAD 內建的 max 函式