# Why doesn't the IEEEtran document class recognize “definition” environments?

I have an IEEEtran document class. I want to put a simple definition inside the document:

\begin{definition}
blab bla
\end{definition}


I am getting the error below:

Environment definition undefined. \begin{definition}

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The class defines no theorem-like environment. Use \newtheorem. –  egreg Jun 26 '12 at 15:14

IEEEtran defines its own environments which is used to replace existing ones (like enumerate, itemize, etc.). However, it doesn't define any definition environment. You can do so by using \newtheorem:

\documentclass{IEEEtran}% http://www.ctan.org/pkg/ieeetran
\newtheorem{definition}{Definition}
\begin{document}
\begin{definition}
Here is a definition.
\end{definition}
\end{document}​

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I prefer to the \theoremstyle{break} in the package ntheorem. However, if I use this in IEEEtran, its theorem/definition numbers are prefixed by the Roman section number (II.5) instead of original Arabic number (2.5). How can I get both 2.5 and the break style? –  hengxin Oct 10 '13 at 13:20
I tried \usepackage[thmmarks]{ntheorem} \theoremstyle{break} \newtheorem{theorem}{Theorem}[section] \renewcommand{\thetheorem}{\arabic{section}.\arabic{theorem}} in IEEEtran and I got only the number "1.0": (1) Roman section numbering (2) no the keyword "Theorem"; (3) counting goes from 0 instead of 1; (4) no break style. Did I make mistakes? BTW, I decided to follow IEEEtran's default environment: (1) Roman section numbering (2) Arabic.Ababic theorem numbering (3) no break style. Thank you all the same. –  hengxin Oct 11 '13 at 1:54
hum, I still prefer to the following theorem environment in IEEEtrans: (1) Roman section numbering (2) with keywords "Theorem"/"Definition" in bold (3) no indent of the keywords (4) Arabic.Arabic theorem numbering (5) with break style (6) counting goes from 1 within each section. So, I am demanding too much. Thanks a lot. –  hengxin Oct 11 '13 at 3:37
@hengxin: I suggest asking a follow-up question. –  Werner Oct 27 '13 at 6:29