# Change chapter format in amsbook

I'm using amsbook documentclass, but the format of chapter title looks like

CHAPTER 1

Preliminaries on A-theory

(in two lines), which I don't like. I want to change it to

Chapter 1. Preliminaries on A-theory

or

Chapter 1

Preliminaries on A-theory

(in two lines).

Also, the format of proof is in textsc which I don't like, I want it to be like "Proof" as in amsart documentclass.

Is there an easy way to fix these problems?

One just needs to patch the relevant pieces in \@makechapterhead and \proof

\documentclass{amsbook}

\usepackage{xpatch}
\makeatletter
\xpatchcmd{\proof}{\scshape}{\itshape}{}{}
\makeatother

\begin{document}
\chapter{foo}
Bar baz
\begin{proof}
bla bla bla
\end{proof}

\end{document}


A solution with etoolbox is possible too, but the second bit would be difficult, because the proof environment takes an optional argument. One might resort to evil trickery like

\expandafter\patchcmd\csname\string\proof\endcsname{\scshape}{\itshape}{}{}


but avoiding this kind of stuff is precisely one of the reasons xpatch was written.

• Perfect, thanks a lot! Jan 28 '20 at 15:28
• Is it easy to change "Chapter 1" to boldface "Chapter 1" (to be of the same looking as the text in chapter title? If this is easy to do, please to add it also in your answer. Jan 28 '20 at 15:30
• @Lao-tzu not nice but \xpatchcmd{\@makechapterhead}{\mdseries\uppercase\@xp}{\bfseries}{}{} should do. Jan 28 '20 at 15:34
• Thanks, quite good, but the "Chapter 1" is smaller than the size of the text in chapter title. Jan 28 '20 at 15:36
• It was also before, but with uppercase you did't notice it. \xpatchcmd{\@makechapterhead}{\normalsize\mdseries\uppercase\@xp}{\bfseries\fontsize{\@xivpt}{18}}{}{}. Jan 28 '20 at 15:38