The close question was asked here. The question I need is in the comments (asked by LaRiFaRi) but never had the answer.
How to change "0.0.Intro" into simple "Intro" in the following MWE?
\documentclass[10pt]{book}%
\usepackage[utf8]{inputenc}
\usepackage{lipsum}
\usepackage[english]{babel}
\usepackage[OT1]{fontenc}
\usepackage{euler,beton}
\usepackage[paperwidth=145mm, paperheight=215mm,inner=1.6cm,top=2.4cm,bottom=4cm,textwidth=7.4cm,marginparwidth=40mm]{geometry}
\usepackage{fancyhdr}
\pagestyle{fancy}
\renewcommand{\headrulewidth}{1pt}
\renewcommand{\footrulewidth}{1pt}
\fancypagestyle{style1}{
\fancyhf{}
\fancyhead[LE,RO]{\bfseries\thepage}
\fancyhead[LO]{\bfseries\rightmark}
\fancyhead[RE]{\bfseries\leftmark}
}
\fancypagestyle{style2}{
\fancyhf{}
\addtolength{\headwidth}{\marginparwidth}
\addtolength{\headwidth}{\marginparsep}
\fancyhead[LE,RO]{\bfseries\thepage}
\fancyhead[LO]{\bfseries\rightmark}
\fancyhead[RE]{\bfseries\leftmark}
}
% Redefine the PLAIN style
\fancypagestyle{plain}{%
\fancyhead{} %Clean headers
\fancyfoot{} %Clean footers
\renewcommand{\headrulewidth}{1pt} % Header rule's width
\fancyhead[LE,RO]{\bfseries\thepage}
\fancyhead[LO]{\bfseries\rightmark}
\fancyhead[RE]{\bfseries\leftmark}
}
\author{A. Uthor}
\title{What is the Title of This Book?}
\date{today}
\begin{document}
\newgeometry{top=24mm,bottom=40mm,inner=16mm,outer=3.2cm}
\pagestyle{style1}
\maketitle
\thispagestyle{empty}
{This page is intentionally left blank}
\newgeometry{top=24mm,bottom=40mm,inner=16mm,outer=3.2cm,marginparwidth=20mm}
\pagestyle{style2}
\tableofcontents
\clearpage{\pagestyle{empty}\cleardoublepage}
\section*{Intro}\sectionmark{Intro}
\addcontentsline{toc}{section}{\textbf{Intro}}
\lipsum
\end{document}


\sectionmarkbut\markright{Intro}or\markboth{Intro}{Intro}.\sectionmarkusually adds\thesectionin front of the title given by the argument. Or put the into into the frontmatter and use\frontmatter\chapter{Intro}…\mainmatter. BTW: KOMA-Script classscrbookprovides command\addchap{…}and\addsec{…}, that would not need additional commands to set the page header or a ToC entry. – Schweinebacke Dec 01 '17 at 13:38