\documentclass[a4paper,12pt]{report}
\usepackage{graphicx} % inserting images
\usepackage{makeidx}
\usepackage{amsthm,amsmath}
\usepackage{amssymb}
\usepackage{mathrsfs}
\usepackage{fancybox}
\usepackage{lscape}
\usepackage{longtable}
%\usepackage[all]{xy}
%\usepackage{setspace}
%\makeindex
\usepackage{hyperref} % PDF links
\usepackage[onehalfspacing]{setspace} % for switching between double/single space in document
\usepackage{fancyhdr} 
% package for changing Headings style
% setting the margins of page
\usepackage[top=2.8cm,right=3.75cm,bottom=2.8cm,left=2.7cm]{geometry}               
%\renewcommand{\baselinestretch}
\usepackage{xepersian}
%\settextfont[Scale=1.3{B Lotus}
% tell tex engine address of folder containing your pictures
\graphicspath{{images/}}
% commands to print the page number in header
%\pagestyle{fancy}
\cfoot{}
\lhead{\thepage}
% commands related to XePersian package
\settextfont[Scale=1.1]{XB Yas}
\setdigitfont{PGaramond}
\setlatintextfont{Times New Roman}
\usepackage{makeidx}
%\linespread{1.3}
\makeindex
%\showidx
\renewcommand{\baselinestretch}{1.8}
%\setlatintextfont{LinLibertine}
% -------------------------------------
%%%%%%%%%%%%%%%numbering theorem,lemma,...
\newtheorem{theorem}{قضیه}[section]
\newtheorem{lemma}[theorem]{لم}
\newtheorem{proposition}[theorem]{گزاره}
\newtheorem{corollary}[theorem]{نتیجه}
\newtheorem{definition}[theorem]{تعریف}
\newtheorem{remark}[theorem]{ملاحظه}
\newtheorem{example}[theorem]{مثال}
\renewcommand\proofname{برهان}
%%Mathematical Operators
\newcommand{\HH}{\mathbb{H}}
%\newcommand{\SS}{\mathbb{S}}
\newcommand{\NN}{\mathbb{N}}
\newcommand{\QQ}{\mathbb{Q}}
\newcommand{\RR}{\mathbb{R}}
\newcommand{\EE}{\mathbb{ٍE}}
\input{jeld_info}
\begin{document}
\include{cover_fa}
%\include{taeid}
%\include{To}
%\include{ack}
%\include{abstract_fa}
\pagenumbering{harfi}
%\pagenumbering{arabic}
{\setlength{\baselineskip}%
{1.8\baselineskip}
\tableofcontents
%\listoffigures
%\listoftables
% insert each of your chapters with a \inlcude{filename} command as below
\doublespacing
\include{intro}
\include{chap1}
\include{chap2}
\include{aims}
%\include{chap3}
%\include{chap4}
%\include{index}
% -----------------------------------------------------------------------
% If do not have appendix then comment following 3 lines
%\appendix
%\include{peyvast1}
%\include{peyvast2}
% -------------------------------------------------------
\singlespacing
\include{reftest2}
{\setlength{\baselineskip}%
{1.8\baselineskip}
\addcontentsline{toc}{chapter}{\textbf{نمایه}}
\printindex
%\include{abstract_en}
%\include{cover_en}
\end{document}