9.4

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9.4

$\begin{proof}Observe that \begin{displaymath}\sum_{C\subseteq A\subseteq D}p^{... ...e{i}}p^iq^{\vert X\vert-i}=(p+q)^{\vert X\vert}=1.\end{displaymath} \end{proof}$

Jukna 2003-01-15