# French Theoremstyle

\documentclass[french]{article}

\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{babel}
\usepackage{amssymb,amsfonts}
\usepackage{amsmath}
\usepackage{amsfonts}

\theoremstyle{definition}

\begin{document}

\end{document}


I am working in a French Environment and I am getting the error "Undefined control sequence. l.12 \theoremstyle {definition}". Most probably Theoremstyle is not defined for the French Environment. How should I write it?

• You need either amsthm or ntheorem. I usually recommend the former. – egreg May 13 '18 at 9:56

You will need to load the package amsthm, I have attached an example below:

\documentclass[french]{article}

\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{babel}
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amsthm}

\theoremstyle{definition}

\newtheorem{theorem}{Théorème}
\newtheorem{lemma}[theorem]{Lemme}
\newtheorem{corollary}[theorem]{Corollaire}
\newtheorem{proposition}[theorem]{Proposition}
\newtheorem{definition}{Définition}
\newtheorem{example}[theorem]{Exemple}
\newtheorem{remark}{Remarque}
\newtheorem{notation}[theorem]{Notation}

\begin{document}
\begin{theorem}
Mon nouveau théorème
\end{theorem}

\begin{proof}
Et voila
\end{proof}

\end{document}


Then you can fine tune how your environments (theorem, definition, corollary, etc) will behave. I have added a few environments in the code above along with their French names.

Hope that helps.

Romain

• I suppose you want to load babel with the french option. – GuM May 13 '18 at 10:16
• @GuM: No, since version 3.10, language options of babel should be loaded with the document class, so all language-dependent packages be informed. – Bernard May 13 '18 at 12:01
• @Bernard: You know what? I didn’t notice the french option passed to the document class… :-) – GuM May 14 '18 at 8:50
• @GuM: Speed reading? ;o) – Bernard May 14 '18 at 8:56
• off topic: sinceamssymb loads amsfonts, it's not necessary to do that separately. – barbara beeton May 14 '18 at 12:10