[Tex/LaTex] Redefining a theorem counter

countersnumberingtheorems

I have a document with a lot of lemmas and theorems. In the main part of the document there are sections and subsections, so I defined

\newtheorem{lem}{Lemma}[subsection]

to number the lemmas accordingly. But in the appendices I don't have subsections, so I figured it would be better if lemmas in the appendices are not numbered with respect to subsections, but with respect to sections. Therefore, I gave the command

\renewcommand\thelem{\thesection.\arabic{lem}}

just after opening the appendices with \appendix. But something strange happened. In appendix A I don't have lemmas. In appendix B the first lemma is numbered B.3. Could anyone explain me this behavior and suggest a solution?

Edit: If I give the command

\renewcommand\thelem{\thesection.\arabic{lem}}
\setcounter{lem}{0}

the first lemma will be numbered B.1. But I'm still confused about why it is necessary to set the counter to 0.

Best Answer

Your counter resets at subsections not at sections, so

\makeatletter
\@addtoreset{lem}{section}
\makeatother

Related Solutions

[Tex/LaTex] Numbering theorems in the appendix by adding the appendix letter in front/after the theorem number

Add the following code to the preamble settings of your LyX document:

\usepackage{chngcntr}

In the document body, add the following "Evil Red Text" (LaTeX code) immediately after \appendix to effect the desired change for an environment called thm:

\counterwithin{thm}{section}
% \renewcommand{\thethm}{\thesection\arabic{thm}}% optional

You'll have to check your preamble for the existing theorem-like environments and their names (AFAIK, this depends on the loaded LyX modules) and apply the above code for every environment.

Here's a compilable example:

\documentclass{article}

\newtheorem{thm}{Theorem}

\usepackage{chngcntr}

\begin{document}

\section{First}

\begin{thm}
A theorem.
\end{thm}

\section{Second}

\begin{thm}
Another theorem.
\end{thm}

\appendix

\counterwithin{thm}{section}
% \renewcommand{\thethm}{\thesection\arabic{thm}}% optional

\section{App-First}

\begin{thm}
An appendix theorem.
\end{thm}

\section{App-Second}

\begin{thm}
Another appendix theorem.
\end{thm}

\end{document}

[Tex/LaTex] Counter on Appendix without sections

This may depend heavily on the package you're using for your theorems/lemmas. However, in the default situation with book and using the traditional \newtheorem command to create your theorems, the following works.

The MWE below renews the display of the section number to only print the chapter number (since the section number is not needed). The image below shows an extract of pages 1 & 3 only:

enter image description here

\documentclass{book}
\usepackage{lipsum}% http://ctan.org/pkg/lipsum
\newtheorem{theorem}{Theorem}[section]
\renewcommand{\thetheorem}{\thesection.\arabic{theorem}}
\begin{document}
\chapter{A chapter}\lipsum[1]
\section{A section}\lipsum[2]
\begin{theorem}\lipsum[3]\end{theorem}
\appendix
\makeatletter
\@addtoreset{theorem}{chapter}% Reset theorem counter with stepping of chapter
\makeatother
\renewcommand{\thesection}{\thechapter}% Section number prints chapter number
\chapter{Another chapter}\lipsum[4]
\begin{theorem}\lipsum[5]\end{theorem}
\end{document}

Counter resetting with the stepping of other counters is achieved via \@addtoreset. However, other packages also provide this functionality, like chngcntr (using \counterwithin and \counterwithout) and amsmath (using \numberwithin and \numberwithout). See the UK TeX FAQ entry Master and slave counters.

Best Answer

Related Solutions

[Tex/LaTex] Numbering theorems in the appendix by adding the appendix letter in front/after the theorem number

[Tex/LaTex] Counter on Appendix without sections

Related Question