\documentclass[a4paper]{book}
\usepackage[greek]{babel}
\usepackage{ucs}
\usepackage[utf8x]{inputenc}
\usepackage[margin=3cm]{geometry}
\usepackage{fancyhdr}
\usepackage{kerkis}
\usepackage{fancyhdr}
\def\lat#1{\textlatin{#1}}
\begin{document}
\tableofcontents
\include{chapter1}
\lat{G.N.U }
\ldots{}
\end{document}