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%% \renewcommand{\chapter}[1]{\chapter[#1]{\centering #1}}
\usepackage{titlesec}
\usepackage{graphicx}
%\titleformat{\chapter}[display]
% Reza 10/9/2015
\titleformat{\chapter}
% {\normalfont\huge\bfseries\centering}{\chaptertitlename\ \thechapter}{20pt}{\Huge}
% Reza 10/9/2015
{\normalfont\huge ...

hey thank u that code works but arrow doesnt show in pdf, how to show the arrow ?

! Package textcomp Error: Symbol \textrightarrow not provided by
(textcomp) font family bch in TS1 encoding.
(textcomp) Default family used instead.

See the textcomp package documentation for explanation.
Type H <return> for immediate help.
...

l.1407 S \textrightarrow
{} A \textrightarrow{} B ...