If $\{a_n\}$ is a sequence such that $0\leq a_{m+n}\leq a_m+a_n$, show that $\lim_{n\to\infty}\frac{a_n}{n}$ exists
Prove $\lim_{n\to\infty} \frac{a_n}{n}$ exists for positive sequence where $a_{n+m} \leq a_n + a_m$