LaTeX-examples/documents/math-theorem/math-theorem.tex

\documentclass[a4paper]{scrartcl}
\usepackage{amssymb, amsmath} % needed for math
\usepackage[utf8]{inputenc} % this is needed for umlauts
\usepackage[ngerman]{babel} % this is needed for umlauts
\usepackage[T1]{fontenc}    % this is needed for correct output of umlauts in pdf
\usepackage{ntheorem}

\theoremstyle{break}
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\newtheorem{theorem}{Theorem}

\begin{document}
Text body. Text body. Text body.

\begin{theorem}[Pythagoras]
    Let $a,b,c$ the sides of a rectangular triangle.
    Without loss of generality, we assume that  $a<b<c$.

    Then, the following equality holds:
           \[a^2 + b^2 = c^2\]
\end{theorem}

More text. And even more text.
\end{document}