example13.tex

\documentclass{book}
\usepackage{lipsum}
\usepackage{boxedminipage}
\usepackage{fancyhdr}
\pagestyle{fancy}
\fancyhead[LE,RO]{\rightmark}
\fancyhead[LO,RE]{\leftmark}
\renewcommand{\chaptermark}[1]
  {\markboth{\thechapter.\ \chaptername.\ #1}{}}

\begin{document}
\chapter{Introduction}

\begin{boxedminipage}{\textwidth}
This is example 13 in the fancyhdr documentation. 
This demonstrates the use of \verb|\chaptermark|.
\begin{verbatim}
\renewcommand{\chaptermark}[1]
  {\markboth{\thechapter.\ \chaptername.\ #1}{}}
\end{verbatim}
\end{boxedminipage}

\section{The Problem}
\label{sec:problem}

\lipsum[1]

\section{Evaluation}

\lipsum[2]

\chapter{Implementation}

Introduction of this chapter

\lipsum[3]

\section{First steps}
\label{sec:first-steps}

\lipsum

\end{document}