I have the following preamble and I want the subsection not to be visible in the text. Instead of Chapter 1 "Blah Blah" I only want "Blah Blah to be visible. With this code I did it bu the subsections are still visible in the text. e.g. 2.5 "blah blah". How can I also remove 2.5 ??
\documentclass[a4paper,12pt]{book}
\usepackage{titlesec}
\titleformat{\chapter}[display]{\normalfont\huge\bfseries}{}{20pt}{\Huge}
\let\cleardoublepage\clearpage
\usepackage[english,greek]{babel}
\usepackage[utf8x]{inputenc}
\usepackage{blindtext}
\usepackage[pdftex]{graphicx}
\usepackage[skip=2pt, font=small, labelformat = empty]{caption}
\newcommand{\gr}{\selectlanguage{greek}}
\newcommand{\en}{\selectlanguage{english}}
\usepackage{wrapfig}
\usepackage[paperwidth=17cm, paperheight=24cm]{geometry}
\usepackage[onehalfspacing]{setspace}
\usepackage{textcomp}
\useshorthands{;}
\defineshorthand{;}{?}
\usepackage{fancyhdr}
\fancyhf{}
\fancyhead[LE]{\nouppercase{\leftmark}}
\fancyhead[RO]{\nouppercase{\rightmark}}
\fancyfoot[LE,RO]{\thepage}
\pagestyle{fancy}
\renewcommand{\chaptermark}[1]{ \markboth{#1}{} }
\renewcommand{\sectionmark}[1]{ \markright{#1}{} }
