Skipping line after "Proof" in proof environment

Question

Like the OP in Is it possible to skip the first line in a theorem environment?, I would like to be able to skip a line after the word "Proof" so that the first line of the proof is actually part of its own paragraph. For whatever reason the \leavevmode command suggested in the answer to the referenced question doesn't always work; it only seems to work whenever the body of the proof consists of an enumeration. I'm just using the amsthm package with the default settings. Is there a command that can be issued at the beginning of the proof that will allow me to skip a line? Of course, like the OP, I've tried \\ and variants thereof and am only rewarded with the obnoxious "There's no line here to end" error.

I'd say that \begin{proof}\mbox{}\\* should do. (I'd never go to a new line, though.) In amsthm the proof environment is not implemented as a theorem-like one (differently from ntheorem), so those advices don't necessary work for proof. — egreg, Dec 01 '11 at 22:07
As suggested by the UK TeX FAQ entry on No line here to end, you could also use \hspace*{\fill}. As @egreg suggests, the implementation of amsthm's proof environment is that of a trivlist. — Werner, Dec 01 '11 at 22:09
If you would like to do this consistently for the whole document, you could define \newenvironment{myproof}{\proof\mbox{}\\*}{\endproof}. — Stefan Kottwitz, Dec 01 '11 at 22:11
@egreg That seemed to do the trick. Would I be better off overall anyway if I transitioned to ntheorem? — 3Sphere, Dec 01 '11 at 22:11
@Stefan: as implicitly pointed out by Gonzalo, proof has an optional argument. — Ulrich Schwarz, Dec 02 '11 at 07:13
@UlrichSchwarz: Thanks, I included support for it and made an answer from this then. — Stefan Kottwitz, Dec 02 '11 at 08:16
@D063520 Thank you, \begin{proof}~ is the easiest and quickest solution — Splines, Nov 14 '22 at 19:36

score 22 · Accepted Answer · answered Dec 01 '11 at 22:13

If this is to apply to all the proof environments in your document, you can redefine the proof environment to add \\* after the proof name has been written; here's such a redefinition (a \mbox{} will be necessary before \\*):

\documentclass{article}
\usepackage{amsthm}
\usepackage{lipsum}% just to generate text for the example

\makeatletter
\renewenvironment{proof}[1][\proofname]{\par
  \pushQED{\qed}%
  \normalfont \topsep6\p@\@plus6\p@\relax
  \trivlist
  \item[\hskip\labelsep
        \itshape
    #1\@addpunct{.}]\mbox{}\\*
}{%
  \popQED\endtrivlist\@endpefalse
}
\makeatother

\begin{document}

\begin{proof}
\lipsum*[1]
\end{proof}

\end{document}

enter image description here

score 12 · Answer 2 · answered Nov 22 '13 at 11:36

12

Use \hfill:

\begin{lemma}
balbla
\begin{proof}
\hfill
\begin{enumerate}
\item one
\item two
\end{enumerate}
\end{proof}
\end{lemma}

answered Nov 22 '13 at 11:36

jan

121

2

I like this solution, since I am needing it only in few cases, not in every proof environment. Thanks for that. – quapka Apr 18 '14 at 20:09
Very simple! :) – Green.H Aug 03 '18 at 16:54

score 10 · Answer 3 · answered Dec 02 '11 at 08:15

Instead of redefining the proof environment, you could define your own, based on proof but leaving the old proof intact, and you need just one line:

\newenvironment{myproof}[1][\proofname]{\proof[#1]\mbox{}\\*}{\endproof}

Using a new name makes also clear, that it's a different proof environment. Further, you are still able to use the original proof in cases when you don't like a line break, for example if the proof would consist of one short equation or a reference.

Complete example:

\documentclass{article}
\usepackage[english]{babel}
\usepackage{blindtext}
\usepackage{amsthm}
\newenvironment{myproof}[1][\proofname]{\proof[#1]\mbox{}\\*}{\endproof}
\begin{document}
\begin{myproof}
\blindtext
\end{myproof}
\begin{myproof}[Proof sketch]
\blindtext
\end{myproof}
\end{document}

proof with line break

Didn't you want to show in the first example, that you still can use the original \begin{proof} environment? Just saying:) — quapka, Apr 18 '14 at 20:11

Ribz · Answer 4 · 2016-12-13T21:05:11.783

Use \ \\ after \begin{proof} like this: \begin{proof}\ \\.

This solution works fine for me with package amsthm.

\documentclass{article} 
\usepackage[english]{babel} 
\usepackage{blindtext} 
\usepackage{amsthm} 

\begin{document} 

    \begin{proof}\ \\ 
        \blindtext 
    \end{proof} 

    \begin{proof}[Proof sketch]\ \\ 
        \blindtext 
    \end{proof} 

\end{document}

You will get something like:

Also, in case you want the new paragraph to be indented, you can start it with the command \indent. The code is as follows.

\documentclass{article} 
\usepackage[english]{babel} 
\usepackage{blindtext} 
\usepackage{amsthm} 

\begin{document} 

    \begin{proof}\ \\ 
        \indent\blindtext 
    \end{proof} 

    \begin{proof}[Proof sketch]\ \\ 
        \indent\blindtext 
    \end{proof} 

\end{document}

In this case, you will get something like:

PS. I borrowed the code from Stefan Kottwitz'answer.

This is simple and memorable, but you have to use \indent to indent. — U2647, May 16 '19 at 11:48

Skipping line after "Proof" in proof environment

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