# How to check for document class in conditionals [duplicate]

Possible Duplicate:
Which documentclass is being used?

I know how to use conditionals in LaTeX, but I need to check what documentclass is being used.

I need to not include a package when I'm using g-brief or g-brief2, so how can check for that?

I tried:

}{%
}{%
\usepackage[a4paper, left=2.5cm, right=2.5cm, top=2cm, bottom=3cm]{geometry}
}}

But I get the following error:

! You can't use `\spacefactor' in vertical mode.
\@->\spacefactor
\@m {}
l.29 \@