# theorem header still not breaking line

The question has been asked before at How can I get a line break in a theorem headline?, but the answers seem not to work for me:

\documentclass[a4paper, twoside]{book}%[a4paper,oneside]
\usepackage[ngerman]{babel}

\usepackage[autostyle]{csquotes}
\usepackage[
backend=biber,
style=numeric,
sortlocale=de_DE,
natbib=true,
url=false,
doi=true,
eprint=false
]{biblatex}
\bibliography{itteerde}

\usepackage{amsthm}

\newtheorem{zeit}{Zeit-online}

\begin{document}

\section{2016-02-22}

\begin{zeit}[A long title as a heading for some commentary at more and longer and now or somewhere it should be broken up instead of leaving the page and it sucks?]
\begin{quote}[Waldeule]
...
\end{quote}

Die...
\end{zeit}

Text...

\end{document}


With amsthm there's nothing special to do in order that the “attribution” part (that is, the optional argument) splits across lines.

The problem, in your case, is the quote environment just at the start. An obscure feature, I'd say. Just add \mbox{} so the quote is seen after the attribution has been typeset.

\documentclass[a4paper, twoside]{book}
\usepackage[ngerman]{babel}

\usepackage{amsthm}

\newtheorem{zeit}{Zeit-online}

\begin{document}

\begin{zeit}[A long title as a heading for some commentary at more and longer and
now or somewhere it should be broken up instead of leaving the page and it sucks?]
\mbox{}
\begin{quote}
A quotation of something
\end{quote}
Some text for the theorem.
\end{zeit}

Some text after the theorem.

\end{document}


• no idea why this is how it is but thx, works. – Erik Itter Feb 22 '16 at 14:14
• @user60625 \begin{zeit} and \begin{quote} fight each other trying to do similar things. As I said, it's a quite obscure feature. You'd get the same with center instead of quote: every environment directly based on trivlist has the defect. – egreg Feb 22 '16 at 14:17