essential discontinuity

Let f(x) be a real-valued function and let a be a number in the domain of f(x). If lim_(x->a) f(x) = ± ∞, lim_(x->a^-) f(x) = ± ∞ or lim_(x->a^+) f(x) = ± ∞, then f(x) has an infinite discontinuity at a.