/usr/share/doc/cadabra/reserved/sum.tex is in cadabra 1.46-4.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 | \cdbreserved{sum}{}
Denotes a generic sum of objects. The parser translates objects
separated by a ``$+$'' symbol tol sums.
The default properties of \verb|\sum| are
\begin{verbatim}
\sum{#}::CommutingAsSum.
\sum{#}::DependsInherit.
\sum{#}::IndexInherit.
\sum{#}::WeightInherit(label=all, type=Additive).
\end{verbatim}
~
\cdbseealgo{sumsort}
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