Beweise die Additionsformel (nk)+(nk+1)=(n+1k+1)\begin{pmatrix}n\\k\end{pmatrix}+\begin{pmatrix}n\\k+1\end{pmatrix}=\begin{pmatrix}n+1\\k+1\end{pmatrix}(nk)+(nk+1)=(n+1k+1)