The language is $S = (a^nb^m | n \geq m)$.
I'm having trouble understanding MyHill Nerode theorem. Basically if I want to use MyHill Nerode theorem to prove $S$ is non-regular, I have to show that there are infinitely many equivalence classes. So in this case if I choose $S = a^n$ is simply not working since $n \geq m$ and thus $a^mb^m \in S$. So I think I have to pick $S = b^m$ and $a^nb^m \in S$ but $a^nb^n \notin S$. Does my assumption accurate or any suggestion?