Let $$f(x) = \frac{x^2 + 4}{x^2 - 4}.$$

Find the equations of the horizontal asymptotes and the vertical asymptotes of $f(x)$. If there are no asymptotes of a given type, enter 'NONE'. If there is more than one asymptote of a given type, give a comma separated list (i.e.: 1, 2,...).

Horizontal asymptote(s): $y =$ Vertical Asymptote(s): $x =$