# Starting a proof with \paragraph

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
• 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

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
• 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

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
}{%
\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:

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
}{%
\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