# How to Number Theorems within a Chapter? [duplicate]

There are lots of theorems and lemmas in my thesis which are being numbered continuously from start to end. I want the numbering to be like Theorem <>.<>. Same for lemmas and corollaries. I am using amsthm and the environments are defined like

\newtheorem{definition}{Definition}
\newtheorem{lemma}{Lemma}


Is there any simple way to get chapter-wise numbering?

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## marked as duplicate by Charles Stewart, Martin Schröder, Jesse, Peter Jansson, Svend TveskægJan 30 at 8:42

–  Papiro Jan 30 at 6:53

Just to show another possibility in case.... (We like hard ways ;)...)

This can also be done with chngcntr package.

\documentclass{book}
\usepackage{amsthm}
\newtheorem{theorem}{Theorem}
\newtheorem{definition}{Definition}
\newtheorem{lemma}{Lemma}

\usepackage{chngcntr}
\counterwithin{theorem}{chapter}
\counterwithin{definition}{chapter}
\counterwithin{lemma}{chapter}
\begin{document}

\chapter{1st chapter}

\begin{theorem}
A theorem
\end{theorem}

\begin{definition}
A definition.
\end{definition}

\begin{lemma}
A lemma.
\end{lemma}

\chapter{2nd chapter}

\begin{theorem}
A theorem
\end{theorem}

\begin{definition}
Another definition.
\end{definition}

\begin{lemma}
Another lemma.
\end{lemma}

\end{document}


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One should go Karl's way though :) –  Harish Kumar Jan 30 at 8:19
Thanks a lot. It works fine for environments except theorem, which is an inbuilt environment. When I add \counterwithin{theorem}{chapter} to my preamble, I get error saying theorem is not a counter. –  Barman Jan 30 at 9:25
@Barman It works for theorems too. See the edit. :) –  Harish Kumar Jan 30 at 9:52

If I understand correctly, you want your theorem-like environments to be numbered within chapters.

To do this, you have to add the optional parameter chapter to your theorem definitions, for example:

\newtheorem{definition}{Definition}[chapter]
\newtheorem{lemma}{Lemma}[chapter]


In this way their number contains the chapter number and the numeration is reset at every chapter.

MWE:

\documentclass{book}
\usepackage{amsthm}

\newtheorem{definition}{Definition}[chapter]
\newtheorem{lemma}{Lemma}[chapter]

\begin{document}

\chapter{1st chapter}

\begin{definition}
A definition.
\end{definition}

\begin{lemma}
A lemma.
\end{lemma}

\chapter{2nd chapter}

\begin{definition}
Another definition.
\end{definition}

\begin{lemma}
Another lemma.
\end{lemma}

\end{document}


Output:

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Thanks, but I want it for theorem like environments and theorems as well. How do I do it for the theorem environment which is already defined? –  Barman Jan 30 at 9:27
@Barman, something like \newtheorem{theorem}{Theorem}[chapter] –  karlkoeller Jan 30 at 9:29
\newtheorem{theorem}{Theorem} says the environment is already defined and gives error. The same problem with @Harish's answer as well. –  Barman Jan 30 at 9:38