When you go to the checkout page you'll get these two variables:
When it is an anonymous checkout then "main will not equal checkout"
When it is a checkout, then "main will not equal anonymous_checkout"
So no matter what, one of the ne statements will be true. You can't use the OR command then, because at any given time one of the statements will be true. If you use the AND then it will work.
Don't know if that makes sense or not
