Interference between amsmath and ntheorem

Question

I am having some problems that `seem' to me to be a conflict between amsmath and ntheorem. Here is a MWE:

\documentclass[12pt,a4paper,oneside]{report}
\usepackage[left=2.00cm,right=2.00cm,top=2.45cm,bottom=2.5cm]{geometry}
\usepackage[amsmath,amstext,thmmarks]{ntheorem}
\usepackage{color,fancyhdr,framed,latexsym,multicols,slashed}

\theoremclass{Theorem}
\theoremstyle{break}
\newframedtheorem{Theorem}[Theorem]{Theorem}

\begin{document}
\begin{Theorem}
Let $X$ be a set with $n$ elements. Then $\mathcal{P}(X)$ is a set with $2^n$ elements.
\end{Theorem}

\end{document}

Ay help would be greatly appreciated. Thanks.

Answer 1

A minimal document that compiles is

\documentclass[a4paper]{report}
\usepackage{amsmath} % necessary for the `amsmath` option
\usepackage{framed}  % necessary for the `\newframedtheorem` command
\usepackage[amsmath,thmmarks,framed]{ntheorem}

\theoremclass{Theorem}
\theoremstyle{break}
\newframedtheorem{Theorem}{Theorem}

\begin{document}
\begin{Theorem}
Let $X$ be a set with $n$ elements. Then $\mathcal{P}(X)$ is a set with $2^n$ elements.
\end{Theorem}

\end{document}

You're making some errors

1. In order to use the amsmath option in ntheorem you have to load amsmath
2. In order to use the \newframedtheorem command defined in ntheorem you have to load framed and pass the framed option.
3. You have a spurious [Theorem] in the definition of the environment.

However, the mdframed package is much more powerful for defining "boxed" theorems. Check its documentation