%\footnote{\l\label{•} abel{•} }
\documentclass[12pt,a4paper]{report}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{makeidx}
\usepackage{exscale}
\usepackage{amsmath, amsthm, amscd, amsfonts, amssymb}
\usepackage{xepersian}
%\usepackage{fancybox}
\usepackage{fancyhdr}
\linespread{ 2.2}
\settextfont[Scale=1.3]{B Badr}
\setdigitfont[Scale=1.3]{B Badr}
\pagestyle{headings}
\makeindex 

\begin{document}
$S$-سیستم
\end{document}