Changing style of Proof

Question

I'm using the \begin{proof} of the amsthm package. And I want to change the style of the Proof word that is added in the beginning. By default it is italic, I want to make it bold. How can I do it?

Answer 1

How about:

\renewenvironment{proof}{{\bfseries Proof}}{*something*}

*something* - something to be executed after environment argument is processed (possibly empty).

More here: http://en.wikibooks.org/wiki/LaTeX/Customizing_LaTeX.

Answer 2

If you don't mind changing the name of the environment, just use a variant of the following code. Change \ttfamily \scshape \large #1 (yes, "#1") to something more sensible: #1 denotes the "Proof" word.

\newenvironment{myproof}[1][\proofname]{%
  \proof[\ttfamily \scshape \large #1 (yes, ``#1'')]%
}{\endproof}

\begin{myproof}
Hi.
\end{myproof}

The proof environment takes one argument and puts it in italics (by default this argument is Proof in English). Our new environment also takes one argument, denoted #1 (with the same default), and feeds it to the proof environment after transforming it a bit (or a lot). Here I decided to write the "proof" word in typewriter small-caps, large, and I even put it twice: "Proof, (yes, 'Proof')". Anything can be done with it.

If you want to redefine the proof environment itself, you can do

\documentclass{article}
\usepackage{amsthm}
\expandafter\let\expandafter\oldproof\csname\string\proof\endcsname
\let\oldendproof\endproof
\renewenvironment{proof}[1][\proofname]{%
  \oldproof[\ttfamily \scshape \large #1 (yes, ``#1'')]%
}{\oldendproof}
\begin{document}
  \begin{proof}[Foobar]
    Some example text.
  \end{proof}
\end{document}

When we redefine the proof environment, we are in fact defining \proof and \endproof. The primitive \let makes \oldproof into an exact copy of what \\proof means initially, so that we can use it for defining \proof. Otherwise, \proof would expand to \proof[...], which would expand to \proof[...], etc, looping forever.

EDIT: revised the last code snippet, which was completely wrong.

Answer 3

A better and simpler solution is to redefine \proofname:

\usepackage{amsthm}
\let\oldproofname=\proofname
\renewcommand{\proofname}{\rm\bf{\oldproofname}}

This is better than redefining the proof environment because the environment goes to considerable lengths to position the \qed mark correctly, and to respect the indentation style used in theorems (which is not necessarily the same as for normal paragraphs). It also works fine with the babel package which is helpful if you work in more than one language, or are writing a style file that might be used with multiple languages.

Answer 4

many of the fonts in the ams document classes and amsthm.sty are "frozen", even though they are changed in publication-specific classes to effect a different style. for the next upgrade of the ams-latex collection, we are considering assigning "logical" names to most such fonts, to simplify the ability to make changes such as the one requested here. the "proofheadfont" will be among the fonts to be generalized.

Answer 5

If you're able and happy to modify your amsthm.sty, then find the command that begins \newenvironment{proof} (close to the end of the file), and change itshape to bfseries.

Alternatively, just paste the following into the preamble of your document:

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

Then the proof environment will behave exactly as before in terms of spacing, optional argument, \qedhere and so on, but you'll have bold rather than italic.