If $\lim \sup _{n \rightarrow \infty} a_n=-\infty$, show that $\left(a_n\right)$ diverges to $-\infty$. If $\lim \sup _{n \rightarrow \infty} a_n=$ $+\infty$, show that $\left(a_n\right)$ has a subsequence that diverges to $+\infty$. What happens if $\liminf _{n \rightarrow \infty} a_n= \pm \infty$ ?