\documentclass{article}
\usepackage{amsmath}
\usepackage{amsxtra}
\usepackage{amssymb}
\usepackage{amsfonts}
\renewcommand{\baselinestretch}{}
\begin{document}
\section{q}
\begin{definition}
e
\end{definition}
\begin{Theorem}
s
\end{Theorem}
\end{document}