\documentclass{article}
\newcommand{\sayhello}{Hello! }
\newcommand{\sayhellob}{And a Hearty Hello, to you! }
\newcommand{\saygoodbye}{Goodbye! }
\newcommand{\saygoodbyeb}{Farewell, Farewell! }
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\begin{document}
\section{Introduction}
An introductory section.
 \section{Conclusion}
And a concluding section.
\end{document}