12

I would like to break a proof into paragraphs, but I don't seem to be able to start a proof with a paragraph.

\documentclass{article}
\usepackage{amsthm}

\begin{document}
\begin{proof}
\paragraph{This bit in bold.} Now this part of the proof.
\end{proof}
\end{document}

It seems to be fine if I insert text before the \paragraph, but otherwise I get the following error:

Something's wrong--perhaps a missing \item.

What is the simplest way to start a proof with a paragraph?

  • Welcome to TeX.SX! You can have a look at our starter guide to familiarize yourself further with our format. – Joseph Wright Jul 7 '13 at 15:36
  • \paragraph is a sectioning command, like \section. If you just want to divide material into paragraphs, use a blank line to separate them: is that what you are after? – Joseph Wright Jul 7 '13 at 15:37
  • 1
    You can also put a ~ before the first instance of \paragraph – Steven B. Segletes Jul 7 '13 at 15:39
  • @JosephWright: I'm after the bold formatting that paragraph gives to the supplied text (I've updated my example to make that clearer). – Roly Jul 7 '13 at 15:41
  • @StevenB.Segletes: thanks. Also just discovered that adding \item before \paragraph has the same effect, although I don't know why. – Roly Jul 7 '13 at 15:41
9

Add an \item or ~ before \paragraph. For example:

\begin{document}
\begin{proof}
\item 
\paragraph{This bit in bold.} Now this part of the proof.
\end{proof}
\end{document}
  • The spacing with this solution is a bit odd, but that does the trick. – Clément Oct 8 '15 at 19:42
  • 1
    You can also use ~ instead of \item – Nubok Jul 25 '16 at 10:38
  • @Nubok Thanks. Just noticed that Steven B. Segletes also mentioned that trick a few years ago. Tweaked the title of the answer to bring attention to that alternative. – Roly Jul 25 '16 at 17:38
6

I think the best way is to define a new environment, let's say breakproof, that acts like proof but starts with a new line after the word "Proof".

So you can write

\documentclass{article}
\usepackage{amsthm}

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

\begin{document}
  \begin{breakproof}
    \textbf{This bit in bold.}
    \newline
    Now this part of the proof.
  \end{breakproof}
\end{document} 

and the result is:

enter image description here

Otherwise, you can redefine the proof environment (bad practice, in my opinion) and use it as before (the result is the same):

\documentclass{article}
\usepackage{amsthm}

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

\begin{document}
  \begin{proof}
    \textbf{This bit in bold.}
    \newline
    Now this part of the proof.
  \end{proof}
\end{document} 
  • Thanks. What are the advantages of this over just adding \item at the beginning of the proof? (This seems to have a similar effect, in that the proof then starts with a newline after "Proof.".) – Roly Jul 7 '13 at 17:05
  • Only aesthetics, for me. But you may have a different opinion, and just use \item inside the normal proof :-) – karlkoeller Jul 7 '13 at 17:45
  • Ok, I accepted your answer, but I also added my own answer below. – Roly Jul 7 '13 at 19:38
  • Karl, looks like you are a mathematician ;) – user11232 Jul 8 '13 at 0:03
  • @HarishKumar These are the same words they told me when I got graduated. Are you sure you weren't there at that time? You know, my memory is going away... – karlkoeller Jul 8 '13 at 4:51

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