Changing the theorem's title style

Question

I need to change the style of the theorem title ( bold and no ponctuation after the title) :

\documentclass[french,a4paper,12pt]{report}
\usepackage{babel}
\usepackage{graphicx}
\usepackage{amsmath,amsfonts,amstext,amssymb}
\usepackage{times}
\usepackage{setspace}
\usepackage{Lettrine}
\usepackage{fancyhdr}
\usepackage{multirow}
\usepackage{pslatex}
\usepackage[T1]{fontenc}
\usepackage[latin1]{inputenc}
\usepackage{array}
\usepackage{enumerate}
\usepackage{color}
\usepackage{version}
\usepackage{newcent}
\usepackage{nestochp}
\usepackage{anysize}
\usepackage{amsthm}
\makeatletter
\g@addto@macro\th@remark{\thm@headpunct{ }}
\makeatother
\theoremstyle{remark}
\newtheorem{Def}{Définition}
\newtheorem*{pre}{Preuve}
\newtheorem{The}{Théorème}
\newtheorem{Lem}{Lemme}
\newtheorem*{Rem}{Remarque}
\newtheorem{pro}{Proposition}
 \numberwithin{equation}{chapter}

When I use the code above I got no ponctuation after the theorem's title but the font is not bold.

How can I fix this?

Answer 1

Since,judging by the use of the remark style in your example code, you want boldfaced head, no punctuation after the head and normal font for the body, you can easily define a new style with those requirements:

\documentclass[french,a4paper,12pt]{report}
\usepackage{babel}
\usepackage{amsthm}    

\newtheoremstyle{mystyle}% name
  {\topsep}% Space above
  {\topsep}% Space below
  {\normalfont}% Body font
  {}% Indent amount
  {\bfseries}% Theorem head font
  {}%Punctuation after theorem head
  {.5em}%Space after theorem head
  {}% theorem head spec
\theoremstyle{mystyle}
\newtheorem{Lem}{Lemme}

 \begin{document}

\begin{Lem}
A test lemma.
\end{Lem}

\end{document}

Answer 2

If you only want theorems with bold title and no punctuation, this should do it:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}

\newtheorem{theorem}{Theorem}

\begin{document}    
    \begin{theorem}
        This is a simple theorem with bold title an no punctuation after the title. 
        As simple as it gets...
        $$a^2+b^2=c^2$$
    \end{theorem}
\end{document}