18 \usetikzlibrary{shapes}

    18 \usetikzlibrary{shapes}

    19 \usetikzlibrary{backgrounds}

    19 \usetikzlibrary{backgrounds}

    20 \usetikzlibrary{decorations,decorations.pathreplacing}

    20 \usetikzlibrary{decorations,decorations.pathreplacing}

    21 \usetikzlibrary{fit,calc,through}

    21 \usetikzlibrary{fit,calc,through}

    22 

    22 

    23 \newtheorem{example}[prop]{Example}

    25 \newtheorem{example}[prop]{Example}

    24 

    26 

    25 \usepackage{color}

    27 \usepackage{color}

    26 

    28 

    27 % idea from tex-overflow

    29 % idea from tex-overflow