# how to change format for numbering statements so that number comes first

I was wondering how the format for numbering statements can be changed so that the statement number precedes the word "Theorem" or "Definition". For example, I use the following code:

\newtheorem{Theorem}[Lemma]{Theorem}
\begin{Theorem} \label{thmOnSomething}
Here is the theorem statement.
\end{Theorem}


The output looks like this:

Theorem 1.2.27 Here is the theorem statement.

How can I change the code so that the output is as follows:

1.2.27. Theorem: Here is the theorem statement.

• Do you load amsthm or any other related package. Please add a complete minimal working example. – Marco Daniel Nov 3 '13 at 8:05
• if you're using amsthm, just insert \swapnumbers before the first \newtheorem. documented in the user's guide: texdoc amsthdoc. – barbara beeton Nov 3 '13 at 8:22

In the base LaTeX the solution may be as follows:

\documentclass{book}

\begin{document}

\chapter{One}
\section{Oneone}

\makeatletter
\def\@begintheorem#1#2{\trivlist
%   \item[\hskip \labelsep{\bfseries #1\ #2}]\itshape}
\item[\hskip \labelsep{\bfseries #2.\ #1:}]\itshape}
\makeatother

\newtheorem{tw}{Theorem}[section]

\begin{tw}
1+1=2
\end{tw}

\section{Twotwo}

\begin{tw}
1+1=2
\end{tw}

\end{document}


Because the style of numbering depends on class, there is a full example with the class book. The main trick is in the line below the commented one.