Change displayed theorem numbering

Question

In my LaTeX document I have used numbered theorems with

\newtheorem{theorem}{Theorem}[section]
\begin{theorem}
......
\end{theorem}

The theorems will be numbered by something like "Theorem 2.1."

My question is: how can I get rid of the last period? I want to print out "Theorem 2.1".

Answer 1

The following solution is based on a straightforward adaptation of this answer by @egreg.

\documentclass{article}
\usepackage{amsthm}
%% Create a new theorem style called 'PlainNoDot':
\newtheoremstyle{PlainNoDot}% name of the style to be used
  {\topsep}% measure of space to leave above the theorem. E.g.: 3pt
  {\topsep}% measure of space to leave below the theorem. E.g.: 3pt
  {\itshape}% name of font to use in the body of the theorem
  {}% measure of space to indent
  {\bfseries}% name of head font
  {}% punctuation between head and body: NONE <-- only diff. from default
  { }% space after theorem head; " " = normal interword space
  {\thmname{#1}\thmnumber{ #2}\thmnote{ (#3)}}
%% Switch the active theorem style to 'PlainNoDot':
\theoremstyle{PlainNoDot}
%% Start creating theorem-like environments:
\newtheorem{theorem}{Theorem}[section]
\begin{document}
\setcounter{section}{2} % just for this example
\begin{theorem} Bla bla bla. \end{theorem}
\end{document}