Same numbering in Theorem and Proof

Question

In my thesis, if number theorem statement is 1.12, proof is coming as 1.13. How to make the number of proof as 1.12?

I use

\theoremstyle{plain}
\newtheorem{theorem}{Theorem}
\newtheorem{corollary}[secn]{Corollary}
\newtheorem{proposition}[secn]{Proposition}
\newtheorem{lemma}[secn]{Lemma}
\newtheorem{problem}[secn]{Problem}
\newtheorem{pd}{Problem Statement}
\newtheorem{proof}[secn]{Proof}
\begin{proof}

\end{proof}

I am getting like this:

Lemma 2.9 ........................................

......................................

Proof 2.10 We have two cases.

This is not working:

\theoremstyle{plain}
\newtheorem{theorem}[secn]{Theorem}
\newtheorem{corollary}[secn]{Corollary}
\newtheorem{proposition}[secn]{Proposition}
\newtheorem{lemma}[secn]{Lemma}
\newtheorem{problem}[secn]{Problem}
\newtheorem{pd}{Problem Statement}
\newtheorem{proof}[secn]{Proof}


\usepackage{ntheorem}
\theoremstyle{plain}
%newtheorem{theorem}{Theorem}[section]
% ...
%\newtheorem{proof}[theorem]{Proof} % 'proof' and 'theorem' use same counter variable

\usepackage{etoolbox}
\AtBeginEnvironment{proof}{\addtocounter{theorem}{-1}}

If you're using amsthm, you don't need to define a proof environment using \newtheorem; it already exists. Are you getting any errors with your current setup? — Werner, Mar 20 '18 at 17:16
traditionally, proofs are not numbered. if you are using amsthm, you can give a theorem a \label (say \label{thm:xxx}) and for the proof (not the one you have redefined, but the original), enter it as \begin{[proof}[Proof of Theorem \ref{thm:xxx}. — barbara beeton, Mar 20 '18 at 17:43
Please, make a minimal example of what you're doing; no need to have 12 theorems, one suffices. — egreg, Mar 20 '18 at 18:29

score 3 · Answer 1 · answered Mar 20 '18 at 23:38

This assigns every proof the number of the immediately preceding statement, but with an optional argument to override it.

\documentclass{article}
\usepackage{ntheorem}

\theoremstyle{plain}
\newtheorem{theorem}{Theorem}[section]
\newtheorem{corollary}[theorem]{Corollary}
\newtheorem{proposition}[theorem]{Proposition}
\newtheorem{lemma}[theorem]{Lemma}
\newtheorem{problem}[theorem]{Problem}
\newtheorem{pd}{Problem Statement}

\theorembodyfont{\normalfont}
\newtheorem{proofinner}{Proof}

\newenvironment{proof}[1][]
 {\if\relax\detokenize{#1}\relax
    % no optional argument
    \renewcommand\theproofinner{\thetheorem}%
  \else
    \renewcommand{\theproofinner}{#1}%
  \fi
  \proofinner}
 {\endproofinner}

\begin{document}

\section{Title}

\begin{theorem}\label{thm:main}
Main theorem
\end{theorem}

\begin{lemma}
Whatever
\end{lemma}

\begin{proof}
Here it is.
\end{proof}

\begin{theorem}
Whatever
\end{theorem}

\begin{proof}
Here it is.
\end{proof}

\begin{proof}[\ref{thm:main}]
Proof of main.
\end{proof}

\end{document}

score 0 · Answer 2 · answered Mar 20 '18 at 19:34

One could manually subtract 1 from the theorem counter after the end of Theorem 1.12 and before the start of the associated proof. This procedure may be automated with the help of the etoolbox package and its \AtBeginEnvironment directive.

(This assumes that the proof environment should always carry the same number as its associated theorem-like environment. If you need to override this on occasion, simply provide an \addtocounter{theorem}{1} statement before \begin{proof}.)

\documentclass{article}
\usepackage{ntheorem}
\theoremstyle{plain}
\newtheorem{theorem}{Theorem}[section]
% ...
\newtheorem{proof}[theorem]{Proof} % 'proof' and 'theorem' use same counter variable

\usepackage{etoolbox}
\AtBeginEnvironment{proof}{\addtocounter{theorem}{-1}}

\begin{document}
\setcounter{section}{1} % just for this example
\setcounter{theorem}{11}

\begin{theorem} bla bla bla \end{theorem}
\begin{proof}   ble ble ble \end{proof}

\end{document}

Same numbering in Theorem and Proof

2 Answers2