I'm trying to play around w/ a negative lookbehind regex, but I can't seem to get it to work in my zshell. Am I doing this wrong?

> 
> echo "Nate or nate" | grep "(\?<!N)a"
> 
> 
> 

This should match the `a` in **nate** but ***NOT*** the `a` in **Nate**...right?