Is there an empty value for the counter in `\newtheorem{xxxx}{xxxx}[empty]`?

Question

I'm trying to set an optional counter in the \newtheorem command based on some input given to a .sty file. Something like

\DeclareOption{empty}{
    \edef\counter{} 
}
\DeclareOption{section}{
    \edef\counter{\detokenize{section}} 
}
\ProcessOptions\relax
\theoremstyle{definition}
\newtheorem{definition}{Definition}[\counter]
\providecommand*{\definitionautorefname}{Definition}

The amsthm package accepts section or chapter in \counter. I, instead, would like to not set a counter by setting \counter to some specific value. I've tried \empty,0 and {} as above.

Of course, I could use a bunch of if's for each \newtheorem and simply set \newtheorem{definition}{Definition} when I don't want to associate any counter. I would like to avoid that painful option, however.

Thanks in advance.

Answer 1

I don't think you should force users of your package to have the numbering of definitions independent on theorems and friends.

There is no reason why an author should be forced to a style such as

Lemma 1
Theorem 1
Theorem 2
Definition 1
Lemma 2
Theorem 3

(maybe with section prefix, but that's irrelevant) instead of the more common and friendly

Lemma 1
Theorem 2
Theorem 3
Definition 4
Lemma 5
Theorem 6

(again with a possible prefix). I hate reading such a cross reference as

see chapter II, part II, paragraph VI

or

chapter V, part III, paragraph II, 2, theorem 2

These are from an actual book, which uses “part” instead of section, “paragraph” for subsection and doesn't name subsubsections. There is no clue whatsoever in the page headers about how to find the referenced theorem.

In your proposed “empty” style, the reader will have no clue as to whether Lemma 2 precedes or follows Theorem 1.

Anyway, if you insist on it (maybe because of strict faculty regulations), the trick is to define your own facility.

\DeclareOption{empty}{\let\package@thmprefix=F}
\DeclareOption{section}{\let\package@thmprefix=T\def\package@thmlevel{section}}
\DeclareOption{chapter}{\let\package@thmprefix=T\def\package@thmlevel{chapter}}
\DeclareOption{empty}{\let\package@thmprefix=F}
\DeclareOption{section}{\let\package@thmprefix=T\def\package@thmlevel{section}}
\DeclareOption{chapter}{\let\package@thmprefix=T\def\package@thmlevel{chapter}}
\ExecuteOptions{empty}
\ProcessOptions\relax
\RequirePackage{amsthm}
\def\package@newtheorem#1#2{%
  \if\package@thmprefix F%
    \newtheorem{#1}{#2}%
  \else
    \newtheorem{#1}{#2}[\package@thmlevel]
  \fi
}
\package@newtheorem{lemma}{Lemma}
\package@newtheorem{theorem}{Theorem}
\theoremstyle{definition}
\package@newtheorem{definition}{Definition}

Here's the test file

\documentclass{book}
\usepackage{package}
%\usepackage[section]{package}
%\usepackage[chapter]{package}
\begin{document}
\chapter{Title}
\section{Title}
\begin{lemma}
Text
\end{lemma}
\begin{theorem}
Text
\end{theorem}
\begin{theorem}
Text
\end{theorem}
\section{Title}
\begin{definition}
Text
\end{definition}
\begin{lemma}
Text
\end{lemma}
\begin{theorem}
Text
\end{theorem}
\end{document}

Output with the empty option (default)

Output with the section option

Output with the chapter option