documentclass[12pt,reqno,a4paper]{amsart}
usepackage{extsizes}
usepackage{blindtext}
textheight 9.3in textwidth 6.5in
calclayout
usepackage{mathtools}

usepackage{amsmath,amsthm,amsfonts,amssymb}
newtheorem{theorem}{Theorem}[section]
newtheorem{corollary}{Corollary}[section]
usepackage{hyperref}
usepackage{mathrsfs}
usepackage[all]{xy}
usepackage[normalem]{ulem}
newtheorem{lemma}{Lemma}[subsection]
newtheorem*{question}{Question}
theoremstyle{definition}
newcommand{mc}{mathcal}
newcommand{mf}{mathfrak}
newtheorem*{solution}{Solution}
newtheorem{definition}{Definition}[section]
newtheorem{remark}{Remark}[section]
newtheorem{proposition}{Proposition}[section]
newtheorem{exercise}{Exercise}
newtheorem{example}{Example}[section]
usepackage{tikz-cd}
usepackage[utf8]{inputenc}
usepackage[english]{babel}
usepackage{datetime}
% renewcommand{baselinestretch}{2}
usepackage{color}
pagestyle{myheadings}
newcommand{xra}{xrightarrow}
newcommand{ra}{rightarrow}
begin{document}

end{document}