Starting theorem version numbering at 1.0 instead of 1.1

Question

How I make the numbering in the following file start at 1.0 instead of 1.1? setcounter{dfnv}{-1} doesn't do anything.

\documentclass[12pt]{article}

\usepackage{amsthm}
\usepackage{amsmath}

\newcounter{dfnq}[section]
\newcounter{dfnv}

\makeatletter
\@addtoreset{dfnv}{dfnq}
\let\thedfnvsaved\thedfnv
\renewcommand{\thedfnv}{\thedfnq.\thedfnvsaved}
\makeatother

%% \makeatletter
%% \@namedef{thedfnv}{\@nameuse{thedfnq}.\arabic{dfnv}}
%% \makeatother

\newtheorem{dfn}[dfnv]{Definition}

\begin{document}

\section{First section}


\stepcounter{dfnq}
% Should display as Definition 1.0
% Actually displays as Definition 1.1
\begin{dfn}
  Version 0 of the definition of foo.
\end{dfn}

% Should display as Definition 1.1
% Actually displays as Definition 1.2
\begin{dfn}
  Version 1 of the definition of foo.
\end{dfn}
\stepcounter{dfnq}

% Should display as Definition 2.0
% Actually displays as Definition 2.1
\begin{dfn}
  Version 0 of the definition of bar.
\end{dfn}

% Should display as Definition 2.1
% Actually displays as Definition 2.2
\begin{dfn}
  Version 1 of the definition of bar.
\end{dfn}
\stepcounter{dfnq}

\end{document}

Full disclosure: this is a continuation of my previous question.

Answer 1

All you need is to subtract 1 to the value of your counter when you use it (in \thedfnv). Here it is done using a temporary counter.

\documentclass[12pt]{article}

\usepackage{amsthm}
\usepackage{amsmath}

\newcounter{dfnq}[section]
\newcounter{dfnv}[dfnq]
\newcounter{tmpcnt}

\renewcommand{\thedfnv}{
\setcounter{tmpcnt}{\value{dfnv}}\addtocounter{tmpcnt}{-1}\thedfnq.\thetmpcnt}


\newtheorem{dfn}[dfnv]{Definition}

\begin{document}

\section{First section}


\stepcounter{dfnq}
% Should display as Definition 1.0
% Actually displays as Definition 1.1
\begin{dfn}
  Version 0 of the definition of foo.
\end{dfn}

% Should display as Definition 1.1
% Actually displays as Definition 1.2
\begin{dfn}
  Version 1 of the definition of foo.
\end{dfn}
\stepcounter{dfnq}

% Should display as Definition 2.0
% Actually displays as Definition 2.1
\begin{dfn}
  Version 0 of the definition of bar.
\end{dfn}

% Should display as Definition 2.1
% Actually displays as Definition 2.2
\begin{dfn}
  Version 1 of the definition of bar.
\end{dfn}
\stepcounter{dfnq}

\end{document}

EDIT: a way to get labels to work correctly

• decouple dfnv form dfnq (not strictly necessary but we'll handle the dependency manually)
• initialize dfnv to -1

• define a command \nextdef that you will call instead of \stepcounter{dfnq} :

  \newcommand{\nextdef}{\stepcounter{dfnq}\setcounter{dfnv}{-1}}

• redefine \thedfnv the good old way:

  \renewcommand{\thedfnv}{\thedfnq.\arabic{dfnv}}

And voilà, should work correctly.

\documentclass[12pt]{article}

\usepackage{amsthm}
\usepackage{amsmath}

\newcounter{dfnq}[section]
\newcounter{dfnv}
\setcounter{dfnv}{-1}

\renewcommand{\thedfnv}{\thedfnq.\arabic{dfnv}}

\def\nextdef{\stepcounter{dfnq}\setcounter{dfnv}{-1}}

\newtheorem{dfn}[dfnv]{Definition}

\begin{document}

\section{First section}


\stepcounter{dfnq}
% Should display as Definition 1.0
% Actually displays as Definition 1.1
\begin{dfn}\label{defa}
  Version 0 of the definition of foo.
\end{dfn}

% Should display as Definition 1.1
% Actually displays as Definition 1.2
\begin{dfn}\label{defb}
  Version 1 of the definition of foo.
\end{dfn}
\nextdef

% Should display as Definition 2.0
% Actually displays as Definition 2.1
\begin{dfn}\label{defc}
  Version 0 of the definition of bar.
\end{dfn}

% Should display as Definition 2.1
% Actually displays as Definition 2.2
\begin{dfn}\label{defd}
  Version 1 of the definition of bar.
\end{dfn}
\nextdef

\ref{defa}

\ref{defb}

\ref{defc}

\ref{defd}

\end{document}

Answer 2

Put \setcounter{dfnv}{\numexpr\value{dfnv}-1\relax} after every occurence of \stepcounter{dfnq}.

\documentclass[12pt]{article}

\usepackage{amsthm}
\usepackage{amsmath}

\newcounter{dfnq}[section]
\newcounter{dfnv}

\makeatletter
\@addtoreset{dfnv}{dfnq}
\let\thedfnvsaved\thedfnv
\renewcommand{\thedfnv}{\thedfnq.\thedfnvsaved}
\makeatother

%% \makeatletter
%% \@namedef{thedfnv}{\@nameuse{thedfnq}.\arabic{dfnv}}
%% \makeatother

\newtheorem{dfn}[dfnv]{Definition}

\begin{document}

\section{First section}


\stepcounter{dfnq}
\setcounter{dfnv}{\numexpr\value{dfnv}-1\relax}
% Should display as Definition 1.0
% Actually displays as Definition 1.1
\begin{dfn}
  Version 0 of the definition of foo.
\end{dfn}

% Should display as Definition 1.1
% Actually displays as Definition 1.2
\begin{dfn}
  Version 1 of the definition of foo.
\end{dfn}
\stepcounter{dfnq}
\setcounter{dfnv}{\numexpr\value{dfnv}-1\relax}
% Should display as Definition 2.0
% Actually displays as Definition 2.1
\begin{dfn}
  Version 0 of the definition of bar.
\end{dfn}

% Should display as Definition 2.1
% Actually displays as Definition 2.2
\begin{dfn}
  Version 1 of the definition of bar.
\end{dfn}
\stepcounter{dfnq}

\end{document}

Answer 3

\setcounter{dfnq}{-1} and follows...