Show that $R(k,l) = R(l,k)$ Let $R(k,l)$ denote the Ramsey number.We proved in class a theorem that says 
$$R(k,l) \leq {k+l-2\choose{k-1}} $$
And supposedly we can use this to show that $R(k,l) = R(l,k)$ for all $k,l \in \mathbb{N}$. However I am not seeing it. I feel like I use should induction, but I'm not sure how. Any suggestions?

$${k+l-2\choose{k-1}}=\frac{(k+l-2)!}{(k-1)!(k+l-2-(k-1))!}=\frac{(k+l-2)!}{(k+l-2-(l-1))!(l-1)!}={k+l-2\choose{l-1}}$$
Thus, $k$ and $l$ are interchangable.
