\documentclass[12pt]{article}
\usepackage[utf8]{inputenc}
\usepackage[LGR,T1]{fontenc}
\usepackage[greek,english]{babel}
\usepackage{alphabeta}
\usepackage{newtxtext}
\usepackage{substitutefont}
\substitutefont{LGR}{\rmdefault}{txr}
\usepackage{amsmath}
\usepackage{amsthm}
\usepackage{varioref}
\usepackage{multicol}
\usepackage{graphicx}
\usepacakge{subfigure}
\usepackage{amsmath,amssymb,isotope}
\usepackage{aythblk}
\usepackage{framed,color}
\usepackage{xcolor}
\usepackage{booktabs}
\usepackage{tcolorbox}
\usepackage{url}
\usepackage{geometry}
\geometry{a4paper}
\setlength\parindent{8mm}
\setlength\parskip{5mm}
\newcommand{\amper}{{\fontspec[Scale=.95]{Gentium Italic}\selectfont\itshape\}}
\usepackage{setspace}


\usepackage{sectsty} 
\usepackage[normalem]{ulem} 
\sectionfont{\rmfamily\mdseries\upshape\Large}
\subsectionfont{\rmfamily\bfseries\upshape\normalsize} 
\subsubsectionfont{\rmfamily\mdseries\upshape\normalsize} 
% package for fancy style headers and footers
\usepackage{fancybox}
\usepackage{fancyhdr}
% PDF SETUP
% ---- FILL IN HERE THE DOC TITLE AND AUTHOR
%\usepackage[unicode]{hyperref}
\usepackage[bookmarks, colorlinks, breaklinks, unicode]{hyperref}  
\hypersetup{linkcolor=black,citecolor=black,filecolor=black,urlcolor=black} 
%%%%%%%%%%%%%%%%MATH constructs %%%%%%%%%%%%%%%%%%%%
\newtheorem{theorem}{ΞΞ΅ΟΟΞ·ΞΌΞ±}[section]
\newtheorem{corollary}{Ξ ΟΟΞΉΟΞΌΞ±}[theorem]
\newtheorem{lemma}{ΞΞ�ΞΌΞΌΞ±}[theorem]
%proof is in amsthm QED renew
\renewcommand\qedsymbol{$\blacksquare$}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% redefine bullet symbols and section style
\renewcommand\thesection{\arabic{section}}
%\renewcommand{\labelitemi}{$\blacktriangleright$}
\renewcommand{\labelitemi}{$\bullet$}
\renewcommand{\labelitemii}{\normalfont\bfseries \textendash}
\renewcommand{\labelitemiii}{$\circ$}
\renewcommand{\labelitemiv}{\textperiodcentered}
% change captions especially for greek language - if the document is in ENGLISH, they should vanish
\addto\captionsenglish{%
\renewcommand\prefacename{Ξ ΟΟΞ»ΞΏΞ³ΞΏΟ}%
\renewcommand\refname{ΞΞ½Ξ±ΟΞΏΟΞ­Ο}%
\renewcommand\abstractname{Abstract}%
\renewcommand\bibname{ΞΞΉΞ²Ξ»ΞΉΞΏΞ³ΟΞ±ΟΞ―Ξ±}%
\renewcommand\chaptername{ΞΞ΅ΟΞ¬Ξ»Ξ±ΞΉΞΏ}%
\renewcommand\appendixname{Ξ Ξ±ΟΞ¬ΟΟΞ·ΞΌΞ±}%
\renewcommand\contentsname{Ξ Ξ΅ΟΞΉΞ΅ΟΟΞΌΞ΅Ξ½Ξ±}%
\renewcommand\listfigurename{ΞΞ±ΟΞ¬Ξ»ΞΏΞ³ΞΏΟ Ξ£ΟΞ·ΞΌΞ¬ΟΟΞ½}%
\renewcommand\listtablename{ΞΞ±ΟΞ¬Ξ»ΞΏΞ³ΞΏΟ Ξ ΞΉΞ½Ξ¬ΞΊΟΞ½}%
\renewcommand\indexname{ΞΟΟΞ΅ΟΞ�ΟΞΉΞΏ}%
\renewcommand\figurename{Ξ£ΟΞ�ΞΌΞ±}%
\renewcommand\tablename{Ξ Ξ―Ξ½Ξ±ΞΊΞ±Ο}%
\renewcommand\partname{ΞΞ­ΟΞΏΟ}%
\renewcommand\enclname{Ξ£ΟΞ½Ξ·ΞΌΞΌΞ­Ξ½Ξ±}%


\renewcommand\ccname{ΞΞΏΞΉΞ½        

                  
\renewcommand\headtoname{Ξ ΟΞΏΟ}%
\renewcommand\pagename{Ξ£Ξ΅Ξ»Ξ―Ξ΄Ξ±}%
\renewcommand\seename{Ξ²Ξ»Ξ­ΟΞ΅}%
\renewcommand\alsoname{Ξ²Ξ»Ξ­ΟΞ΅ Ξ΅ΟΞ―ΟΞ·Ο}%
\renewcommand\proofname{ΞΟΟΞ΄Ξ΅ΞΉΞΎΞ·}%
\renewcommand\glossaryname{ΞΞ»ΟΟΟΞ¬ΟΞΉ}%
                                            }

