I modified the chapter title to be shown as 1. ..., but the headings still show CHAPTER.
How can I remove the chapter in headings? Is there a way to modify the chapter style in the contents and heading at the same time?

\documentclass[12pt,oneside]{memoir}
\usepackage{lipsum}
\title{Document}
\author{prosseek}
% }
% http://tex.stackexchange.com/questions/97465/modify-default-memoir-chapter-style
\makeatletter
\newcommand{\fonttitle}{\chaptitlefont}
\makechapterstyle{mystyle}{%
\def\chapterheadstart{\vspace*{\beforechapskip}}
\def\printchaptername{}
\def\printchapternum{}
\def\printchapternonum{}
\def\printchaptertitle##1{\fonttitle \space \fonttitle \thechapter.\space \fonttitle ##1}
\def\afterchaptertitle{\par\nobreak\vskip \afterchapskip}
}
\makeatother
\chapterstyle{mystyle}
\begin{document}
\maketitle
\tableofcontents
\chapter{The Domain Problem and Stakeholders}
\section{First}
\lipsum
\end{document}