& =\left( \frac{1}{\qi{2n-1}} - \frac{\qi{2} }{\qi{2n-1} \qi{2}} \right)
\begin{tikzpicture}[baseline]
    \clip (-1,-1.3) rectangle (1,1.3);

    \node at (0,.6) (top) [ellipse,draw] {$ \hspace{.15 cm} S \hspace{.15cm} $};
    \node at (0,-.6) (bottom) [ellipse,draw]{$ \hspace{.15 cm} S \hspace{.15cm} $};
    \filldraw (top.180) circle (.5mm);
    \filldraw (bottom.180) circle (.5mm);    

    \node at (top.0) (invisible) [right] {};
    \draw (invisible.90)--++(90:2cm);
    \draw (invisible.90) -- ++ (-90:2cm);

    \draw (top.35) -- ++(90:1cm);
    \draw (top.60) -- ++(90:1cm);
    \node at (-.1,1.2) {...};
    \draw (top.145) -- ++(90:1cm);

    \draw (bottom.-35) -- ++(-90:1cm);
    \draw (bottom.-60) -- ++(-90:1cm);
    \node at (-.1,-1.2) {...};
    \draw (bottom.-145) -- ++(-90:1cm);
\end{tikzpicture} \\
& =0.
