$\displaystyle f(x) = \frac{x^2-1}{x^2+1}$.

If there is more than one answer, enter your answers as a comma separated list. If there is no solution, enter NONE. Do not leave a blank empty.

(a) The function has x-intercept(s) at $x =$ help (numbers)

(b) The function has y-intercept(s) at $y =$ help (numbers)

(c) The function has vertical asymptote(s) when $x =$ help (numbers)

(d) The function has horizontal asymptote(s) when $y =$ help (numbers)