# Counter for the Theorem and Lemma

In an article, I need the counter for Theorems (Lemmas), like Theorem X.Y. But, somewhere I do not need the counter for the Theorems, for example: in preface/appendix or somewhere else like Theorem.

Q: How to define the environment for the Theorem or Lemma.

With amsthm you can define a new theorem environment using

\newtheorem{theorem}{Theorem}


If you want an unnumbered version similar to this, then use

\newtheorem*{theorem*}{Theorem}


Use the theorem* environment inside the preface or appendix, and theorem elsewhere. Here is a minimal example:

\documentclass{article}

\usepackage{amsthm}

\newtheorem*{theorem*}{Theorem}
\newtheorem{theorem}{Theorem}

\begin{document}

\begin{theorem}
This is a numbered theorem.
\end{theorem}

\begin{theorem*}
This is an unnumbered theorem.
\end{theorem*}

\end{document}