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@@ -0,0 +1,33 @@
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+\documentclass{article}
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+\usepackage[pdftex,active,tightpage]{preview}
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+\setlength\PreviewBorder{2mm}
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+
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+\usepackage{amssymb,amsmath}
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+\usepackage{pgfplots}
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+
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+\begin{document}
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+\begin{preview}
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+\begin{tikzpicture}
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+ \begin{axis}[
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+ axis lines=middle,
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+ width=15cm, height=15cm, % size of the image
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+ grid = both,
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+ grid style={dashed, gray!30},
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+ enlargelimits=true,
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+ xmin=-1, % start the diagram at this x-coordinate
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+ xmax= 1, % end the diagram at this x-coordinate
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+ ymin= 0, % start the diagram at this y-coordinate
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+ ymax= 1, % end the diagram at this y-coordinate
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+ /pgfplots/xtick={-1,-0.8,...,1}, % make steps of length 0.2
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+ /pgfplots/ytick={0,0.1,...,1}, % make steps of length 0.1
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+ axis background/.style={fill=white},
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+ ylabel=y,
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+ xlabel=x,
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+ legend style={at={(0.8,0.8)}, anchor=north}]
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+ \addplot[domain=-1:1, ultra thick,samples=100,red] {1};
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+ \addplot[domain=-1:1, ultra thick,samples=100,blue] {0};
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+ \legend{$1 \text{, if } x \in \mathbb{Q}$, $0 \text{, if } x \in \mathbb{R} \setminus \mathbb{Q}$}
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+ \end{axis}
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+\end{tikzpicture}
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+\end{preview}
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+\end{document}
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