Numbering theorem-like environments

Question

I would like all my theorem-like environments (theorem, example, etc.) to be numbered but such that the number appears before the environment's name, more or less like this:

1. Theorem

2. Example

How can I do this?

Werner · Accepted Answer

amsthm provides swapnumbers which reverses the display of Theorem . to Theorem. Here's a minimal example: documentclass{article} usepackage{amsthm}% http://ctan.org/pkg/amsthm swapnumbers % Switch number/label style theoremstyle{plain} newtheorem{theorem}{Theorem} newtheorem{example}[theorem]{Example} begin{document} begin{theorem} This is a theorem. end{theorem} begin{example} This is an example. end{example} end{document} In the above example, the example environment shares the theorem counter. Moreover, both are defined with the plain style. There are others available, as shown in the amsthm package documentation.

cmhughes · Answer

There are few ways to create theorem like environments. Here's an option using ntheorem

The trick is to make a new theoremstyle using the arguments

##1 which is the name of the theorem
##2 which is the number of the theorem
##3 which is the optional title of the theorem

Using the examples in the ntheorem documentation as a guide, you can tweak this to suit your needs.

documentclass{article}

usepackage{lipsum}
usepackage{ntheorem}

makeatletter
newtheoremstyle{numberfirst}%
{item[theorem@headerfont{##2theorem@separatorhskiplabelsep ##1}]}%
{item[theorem@headerfont{##2theorem@separatorhskiplabelsep ##1} (##3)]}%
makeatother

theoremstyle{numberfirst}
theoremseparator{.}
newtheorem{mytheorem}{Theorem}

begin{document}

begin{mytheorem}
lipsum[1]
end{mytheorem}

begin{mytheorem}[Optional title]
lipsum[1]
end{mytheorem}

end{document}

barbara beeton · Answer

amsthm has a command swapnumbers that, when specified before the theoremstyle or newtheorem elenments for which numbers are to come first, will do what you want.
for details, see the amsthm user's guide, section 4.2 on "number swapping".

Numbering theorem-like environments

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