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I was wondering whether it is possible to execute a command depending on the used documentclass.

\documentclass{dinbrief}
%\documentclass[a4paper]{letter}
\usepackage{ifthen}

\begin{document}
\ifthenelse{<documentclass is dinbrief>}{\setlength{\headheight}{20mm}}{}
\the\headheight
\end{document}

I think in principle this code should work. But what exactly should go in the conditional of the ifthenelse (instead of ). Via google I could not find out if there is a variable holding the documentclass so can it be requested during compilation, and if it exists, what's its name?

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