Re: theorem

[Paul Smith]

Eric Delevaux wrote:
I reached it, but the first problem is that it's in english, and i >
write in french...
The package ntheorem.sty will help you regarding that problem.
thanks for reply
Could you be more explcit please? I'm really totally new to lyx (and latex).
Eric,
Even without the package ntheorem, you can get what you are wanting by 
adding the following lines to the preamble (Layout-->Document-->Preamble):

\newtheorem{theorem}{ThÃorÃme}[section]
\let\thm\theorem
The above for article AMS. For book AMS, replace section with chapter.
Paul