# Automatically start a new line at the beginning of a proof environment?

I use amsmath to provide the proof environment. However, if a itemize (or tikzpicture) environment immediately follows the proof environment, xelatex will produce a messy result:

\begin{proof}
\begin{itemize}
\item 1
\item 2
\end{itemize}
\end{proof}


Will produce something like this:

Proof. * 1

• 2

So I have to manually add a \mbox after the proof env. Is it possible to make proof automatically add a newline in these situations?

• In my opinion it's better not to format a proof as an itemized or enumerated list. Just add at the beginning of the paragraph a marker (for instance the number of the substatement, or a symbol such as ($\Rightarrow$)). Having a long (or even short) proof with a shifted margin makes for bad pages. – egreg Apr 28 '13 at 10:14
• Related: tex.stackexchange.com/questions/36851/… and tex.stackexchange.com/questions/85059/… (so that this helps someone searching!) – kan Apr 28 '13 at 10:22
• These two questions asked for a newline without any condition. I want to have a 'smart' proof: only add a new line when the first 'thing' inside the proof is itemize, enumerate, description, tikzpicture, or something like these environments. Seems I did not make it clear in the first place. Sorry about that. – capsensitive Apr 29 '13 at 7:04
• @egreg That is a good advice. But sometimes I need to start proof with a tikzpicture, and without \mbox{}, the tikzpicture will float at the top of the proof environment: – capsensitive Apr 29 '13 at 7:07

You can redefine the proof environment and add a \mbox:

\documentclass[a5paper]{article}
\usepackage{amsmath,amsthm}
\makeatletter
\renewenvironment{proof}[1][\proofname]{\par
\pushQED{\qed}%
\normalfont \topsep6\p@\@plus6\p@\relax
\trivlist
\item[\hskip\labelsep
\itshape
}{%
\popQED\endtrivlist\@endpefalse
}
\makeatother
\begin{document}
\begin{proof}
\begin{itemize}
\item 1
\item 2
\end{itemize}
\end{proof}
\end{document}

• But this code seems always add a \mbox{}. Is it possible to add \mbox{} only when it is needed (such as itemize immediately after proof? – capsensitive Apr 29 '13 at 7:01
• @capsensitive: Indeeed. But in a normal case (without a par or empty line) it should work. – Marco Daniel Apr 29 '13 at 8:03
• I see. That really is the perfect solution for me. Thanks. – capsensitive Apr 29 '13 at 8:19
• It's not a good suggestion to manually redefine an enviornment which is often the result of complicated package work... – einpoklum Jun 14 '17 at 18:34