added halfspace image

tikz/topology-halfspace/Makefile

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+SOURCE = topology-halfspace
+DELAY = 80
+DENSITY = 300
+WIDTH = 512
+
+make:
+	pdflatex $(SOURCE).tex -output-format=pdf
+	make clean
+
+clean:
+	rm -rf  $(TARGET) *.class *.html *.log *.aux *.data *.gnuplot
+
+gif:
+	pdfcrop $(SOURCE).pdf
+	convert -verbose -delay $(DELAY) -loop 0 -density $(DENSITY) $(SOURCE)-crop.pdf $(SOURCE).gif
+	make clean
+
+png:
+	make
+	make svg
+	inkscape $(SOURCE).svg -w $(WIDTH) --export-png=$(SOURCE).png
+
+transparentGif:
+	convert $(SOURCE).pdf -transparent white result.gif
+	make clean
+
+svg:
+	#inkscape $(SOURCE).pdf --export-plain-svg=$(SOURCE).svg
+	pdf2svg $(SOURCE).pdf $(SOURCE).svg
+	# Necessary, as pdf2svg does not always create valid svgs:
+	inkscape $(SOURCE).svg --export-plain-svg=$(SOURCE).svg

tikz/topology-halfspace/Readme.md

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+Compiled example
+----------------
+![Example](topology-halfspace.png)

tikz/topology-halfspace/topology-halfspace.tex

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+\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}