How to check which Emacs I am using?

Question

I have two Emacs (Aquamacs and text-based Emacs) on my Mac.

In my .emacs file, I can check if I'm using Aquamacs with ...

(boundp 'aquamacs-version)

How can I check if I'm using text based emacs?

EDIT

Jürgen H?tzel's answer works, but for text based emacs, using

(unless (null window-system) ...) 

is better as (window-system) is not defined.

question from:https://stackoverflow.com/questions/4630590/how-to-check-which-emacs-i-am-using