1

I'm writing a mathematics paper with \documentclass{amsart}, and I would like my theorems, definitions, propositions, etc., to be numbered "like subsections", i.e., if a given theorem is the fourth in section 3, it should be called Theorem 3.4.

The usual way to do this seems to be the following:

\newtheorem{theorem}[subsection]{Theorem} \newtheorem{proposition}[subsection]{Proposition} \newtheorem{definition}[subsection]{Definition} ...

That is, the counter used by the theorem, proposition, definition, etc environments is the default subsection counter.

The problem with this, however, is that it interferes with subsection numbering. For example:

  1. Suppose that I'm in section 3.
  2. Then, I start a subsection, which is appropriately called section 3.1.
  3. Then, the first theorem I type will be called 3.2, but since it is actually the first theorem in section 3, I feel it should be called theorem 3.1.
  4. If, after that, I start another subsection, it will be called section 3.3, but since it is the second subsection, I feel it should be called section 3.2 instead... and so on.

The solution I imagined for this was to create another counter that works exactly like subsection but independent of it, but I have failed to do this. I am only able to create new counters that use one number, not "nested" counters, like subsection or subsubsection, if that makes any sense. Any help in doing that or other solutions to my problem would be greatly appreciated.

2
  • You should not use subsection as the driving counter then.
    – user31729
    Commented Jan 17, 2015 at 15:29
  • \newtheorem{theorem}{Theorem}[section]. Are you sure you want theorems, propositions and definitions to be numbered separately?
    – egreg
    Commented Jan 17, 2015 at 15:33

1 Answer 1

5

Probably you want something like

\newtheorem{theorem}{Theorem}[section]
\newtheorem{proposition}[theorem]{Proposition} 
\newtheorem{definition}[theorem]{Definition}

That is number theorem within section and the others to follow the same numberation of theorem

MWE

\documentclass{amsart}

\newtheorem{theorem}{Theorem}[section]
\newtheorem{proposition}[theorem]{Proposition} 
\newtheorem{definition}[theorem]{Definition}

\begin{document}
\section{A section}
\subsection{A subsection}
\begin{theorem}
A theorem
\end{theorem}
\begin{proposition}
A proposition
\end{proposition}
\subsection{Another subsection}
\begin{definition}
A definition
\end{definition}
\end{document} 

enter image description here

If you, instead, want different counters for different types of theorems, use

\newtheorem{theorem}{Theorem}[section]
\newtheorem{proposition}{Proposition}[section]
\newtheorem{definition}{Definition}[section]

MWE

\documentclass{amsart}

\newtheorem{theorem}{Theorem}[section]
\newtheorem{proposition}{Proposition}[section]
\newtheorem{definition}{Definition}[section]

\begin{document}
\section{A section}
\subsection{A subsection}
\begin{theorem}
A theorem
\end{theorem}
\begin{proposition}
A proposition
\end{proposition}
\subsection{Another subsection}
\begin{definition}
A definition
\end{definition}
\end{document} 

enter image description here

3
  • You were quicker ;-)
    – user31729
    Commented Jan 17, 2015 at 15:47
  • Awesome, this is exactly what I wanted. Commented Jan 17, 2015 at 16:55
  • @RaisinBread Glad to help. Commented Jan 17, 2015 at 18:45

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