# Organize counter (newtheorem)

I'm writing some notes and I have a problem with the organization. I defined the theorems as follows:

\documentclass[12pt,a4paper]{book}

\theoremstyle{plain}
\newtheorem{teo}{Teorema}[chapter]
\newtheorem{theo}[teo]{Theorem}
\newtheorem{coro}[teo]{Corolary}
\newtheorem{lema}[teo]{Lemma}
\newtheorem{prop}[teo]{Proposition}

\theoremstyle{definition}
\newtheorem{df}[teo]{Definition}
\newtheorem{ex}[teo]{Example}
\newtheorem{obs}[teo]{Remark}

\begin{document}

\end{document}


In the text, theorems, definitions, propositions etc are in the same "counter". I mean

Theorem 1.5

Proposition 1.6

Example 1.7

I want to organize as follows:

\documentclass[12pt,a4paper]{book}

\theoremstyle{plain}
\newtheorem{teo}{Teorema}[chapter]
\newtheorem{theo}[teo]{Theorem}
\newtheorem{coro}[teo]{Corolary}
\newtheorem{lema}[teo]{Lemma}
\newtheorem{prop}[teo]{Proposition}

\theoremstyle{definition}
\newtheorem{df}[teo]{Definition}
\newtheorem{ex}[teo]{Example}
\newtheorem{obs}[teo]{Remark}

\begin{document}

\chapter{ONE}

\section{1}

Proposition 1
Theorem 1

\section{2}

Theorem 2
Example 1

\chapter{TWO}

\section{1}

Proposition 1
Theorem 1

\section{2}

Theorem 2
Example 1

\end{document}


Is it possible to do that?

• If I understand well, all theorem-like environment should each have its own counter, which should be reset per chapter? – Bernard Dec 2 '18 at 23:03
• @Bernard, yes, exactly! I did not want the theorems to be linked sections, only chapters, but I don't want to use the chapter counter too, I mean "Theorem 1.1". Just "Theorem 1" and restarting in each chapter. – Lucas Corrêa Dec 2 '18 at 23:58

Here you are: remove the optional [teo] everywhere, replace the optional [section]with[chapter], and redefine\theteo, &c., so it doesn't include the chapter number as a prefix.

\documentclass[12pt,a4paper]{book}
\usepackage{amsthm}
\theoremstyle{plain}
\newtheorem{teo}{Teorema}[chapter]
\newtheorem{theo}{Theorem}[chapter]
\newtheorem{coro}{Corollary}[chapter]
\newtheorem{lema}{Lemma}[chapter]
\newtheorem{prop}{Proposition}[chapter]

\renewcommand{\theteo}{\arabic{teo}}
\renewcommand{\thetheo}{\arabic{theo}}
\renewcommand{\thecoro}{\arabic{coro}}
\renewcommand{\thelema}{\arabic{lema}}
\renewcommand{\theprop}{\arabic{prop}}

\theoremstyle{definition}
\newtheorem{df}{Definition}[chapter]
\newtheorem{ex}{Example}[chapter]
\newtheorem{obs}{Remark}[chapter]
\renewcommand{\thedf}{\arabic{df}}
\renewcommand{\theex}{\arabic{ex}}
\renewcommand{\theobs}{\arabic{obs}}

\begin{document}

\chapter{ONE}

\section{1}
\begin{prop}
Proposition 1
\end{prop}
\begin{theo}
A first theorem
\end{theo}

\section{2}

\begin{theo}
Another theorem
\end{theo}
\begin{ex}
A funny example.
\end{ex}

\chapter{TWO}

\section{1}

\begin{prop}
Another proposition.
\end{prop}

\begin{theo}
A first theorem in chap. two
\end{theo}

\section{2}

\begin{theo}
A second theorem in chap. two
\end{theo}
\begin{ex}
A silly example.
\end{ex}

\end{document}


• I got it, perfect! Thank you! A curiosity: using rennewcommand, is possible remove the numbers of theorem-like? – Lucas Corrêa Dec 3 '18 at 0:38
• I think you should define a new theorem style. Package thmtools may help. Other than that, ntheorem has built-in nonumberplain and nonumberbreak` theorem styles. – Bernard Dec 3 '18 at 0:45