LaTeX-examples/tikz/topology-halfspace/topology-halfspace.tex

\documentclass[varwidth=true, border=2pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{patterns}

\begin{document}
    \begin{tikzpicture}
        \draw [white,step=0.5cm, pattern=north east lines] (0,0) rectangle (2,1);
        \draw[very thick] (0,0) -- (2,0);

        \node at (2.4,0.5) {$\stackrel{\sim}{=}$};

    \begin{scope}[shift={(4,0)}]
        \draw[white,pattern=north east lines] ([shift={(180:1cm)}]-0.0,0) arc (180:0:1cm);
        \draw[very thick] (-1,0) -- (1,0);
    \end{scope}
    \end{tikzpicture}
\end{document}