[Zope] expression evaluation in dtml

hi there, I <dtml-in...> over a ZSQL-method and get a variable named auth_user from the database I am accessing. When I do a <dtml-var auth_user>, it renders 'andyman', as I expected. Now, when I do a <dtml-var "REQUEST.AUTHENTICATED_USER">, it also renders 'andyman'. But when I then do a <dtml-if "REQUEST.AUTHENTICATED_USER == auth_user "> Hello </dtml-if>, nothing happens, and that is not what I am expecting. Can anybody please explain and help me out? andyman