How to remove the decimal point at the end of ams thm environment?

Question

My professor's lecture notes

When I use amsthm, the default behaviour is

The minimal working example is as follows:

\documentclass{article}
\usepackage{amsmath,amsthm}
\newtheorem{example}{Example}[section] % parent counter setting
\newtheorem{definition}{Definition}[section]
\begin{document}
\section{Topological space: concepts and examples}
\setcounter{definition}{-1}
\begin{definition}
Let $X$ be a non-empty set. The power set of $X$, denoted as $2^{X}$ is $\{Y|Y\subseteq X\}$
\end{definition}
\setcounter{example}{-1}
\begin{example}
$X=\{1,2\},2^X=\{\{1\},\{2\},\{1,2\},\emptyset\}$
\end{example}
\begin{example}[Euclidean topology]
Let
\end{example}
\setcounter{example}{3}
\begin{example}
Let
\end{example}
\end{document}

Answer 1

You could redefine the theorem style:

\documentclass{article}
\usepackage{amsmath,amsthm}
\newtheorem{example}{Example}[section] % parent counter setting
\newtheorem{definition}{Definition}[section]

\newtheoremstyle{plain}
  {\topsep}   % ABOVESPACE
  {\topsep}   % BELOWSPACE
  {}       % BODYFONT
  {0pt}       % INDENT (empty value is the same as 0pt)
  {\bfseries} % HEADFONT
  {}         % HEADPUNCT
  {5pt plus 1pt minus 1pt} % HEADSPACE
  {}          % CUSTOM-HEAD-SPEC

\begin{document}
\section{Topological space: concepts and examples}
\setcounter{definition}{-1}
\begin{definition}
Let $X$ be a non-empty set. The power set of $X$, denoted as $2^{X}$ is $\{Y|Y\subseteq X\}$
\end{definition}
\setcounter{example}{-1}
\begin{example}
$X=\{1,2\},2^X=\{\{1\},\{2\},\{1,2\},\emptyset\}$
\end{example}

\begin{example}[Euclidean topology]
Let
\end{example}
\setcounter{example}{3}
\begin{example}
Let
\end{example}
\end{document}