% Author: Prof. Dr. Matthias Jung, DL9MJ
% Year: 2023
\begin{tikzpicture}
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    \node at (a.east) [rectangle, draw, anchor=west, minimum height=0.6cm, minimum width=0.6cm, fill=gray!50](b){\texttt{1}};
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    \node at (o.east) [rectangle, draw, anchor=west, minimum height=0.6cm, minimum width=0.6cm](p){\texttt{1}};

    \node at(d.south east)[anchor=south east](){\tiny\texttt{a}};
    \node at(f.south east)[anchor=south east](){\tiny\texttt{b}};
    \node at(g.south east)[anchor=south east](){\tiny\texttt{c}};
    \node at(h.south east)[anchor=south east](){\tiny\texttt{d}};
    \node at(j.south east)[anchor=south east](){\tiny\texttt{e}};
    \node at(k.south east)[anchor=south east](){\tiny\texttt{f}};
    \node at(l.south east)[anchor=south east](){\tiny\texttt{g}};
    \node at(m.south east)[anchor=south east](){\tiny\texttt{h}};
    \node at(n.south east)[anchor=south east](){\tiny\texttt{i}};
    \node at(o.south east)[anchor=south east](){\tiny\texttt{j}};
    \node at(p.south east)[anchor=south east](){\tiny\texttt{k}};
\end{tikzpicture}