\documentclass[11pt]{book} \usepackage{indentfirst} \usepackage[colorlinks]{hyperref} \usepackage[pdftex]{graphicx} \usepackage[mathscr]{eucal} \usepackage{vntex} \usepackage[charter]{mathdesign} \usepackage[left=3.25cm,right=2.4cm,bottom=2.4cm,top=3cm]{geometry} \usepackage{fancybox} \newtheorem{problem}{Bài toán} \newcommand{\bp}{\bigskip \begin{problem} } \newcommand{\ep}{\end{problem}} \newcommand{\bs}{\begin{proof}[\textbf{Proof}]} \newcommand{\es}{\end{proof}} \newcommand{\sym}{\centerline{$\star\bigstar\star$}} \newcommand{\dsum}{\displaystyle\sum} \newcommand{\dprod}{\displaystyle\prod} \parindent 0pt \pagestyle{myheadings} \begin{document} Võ Quốc Bá Cẩn \end{document}